Expandable fixation assemblies

ABSTRACT

Expandable fixation assemblies, expandable cranial fixation assemblies, and expandable intervertebral implant assemblies are provided for securing structures to bone and for securing bones and/or bone segments with respect to each other. An expansion member can be moved through at least a portion of an expandable fixation body, thereby causing expansion of the expandable fixation body, such that bone engagement features of the expandable fixation body engage surrounding structure, such as bone.

CROSS-REFERENCE TO RELATED APPLICATIONS

This patent application is a divisional application of U.S. patentapplication Ser. No. 12/831,144, filed Jul. 6, 2010, which claims thebenefit of U.S. provisional patent application No. 61/223,261, filedJul. 6, 2009, the teachings of all of which are incorporated herein byreference in their entirety.

TECHNICAL FIELD

The present disclosure relates generally to fixation members, and inparticular to expandable fixation members for fastening a structure tobone and/or for securing bone segments.

BACKGROUND

Bone screws are commonly used to fix adjacent bones or bone fragmentswith respect to each other, or to attach structure to bone. For example,bone screws are commonly used to help repair fractures in bone, toattach bone plates to bone, to fix adjacent vertebral bodies, and so on.

However, typical bone screws and conventional methods of bone screwinsertion can introduce undesirable complications in such procedures.For example, conventional methods of bone screw insertion can lead to:small and/or mobile bone fragments dislocating from the bone or bonesegment due to axial pressure and insertion torque transmission duringscrew insertion; screw loss during operation (including transporting thescrew from its storage place to final fixation location in the patient);shear off and cam out of the screw head during screw insertion and/orremoval; slipping between the screw driver interface and the screwdriver; stripping of the screw driver interface; bone milling duringrotational insertion of self drilling and/or self tapping screws;misalignment of the pre-drilled holes in adjacent bone fragments and/orbone plates which can lead to secondary dislocation and inaccuratepositioning of the bone fragments and/or bone plate; suboptimal screwfixation due to angular misalignment of a pre-drilled pilot hole's axisand the desirable screw insertion axis; and post operative back out ofscrews. Furthermore, when conventional bone screws are used to attachsmall bone segments that have little structural support, the axial androtational force required to start a screw into such small fragments canbe such that the fragment becomes dislocated. Additionally, when it isdesirable to use a long bone screw, driving the screw into bone canbecome laborious.

Additional complications of using typical bone screws and conventionalmethods of bone screw insertion can be introduced by the sheer number ofsteps, and associated opportunities to introduce errors, required in agiven procedure. For instance, in the case of a bone fracture, FIG. 1Aillustrates a conventional bone lag screw 10 with a partially threadedshaft that is used to join two fractured bone segments 11 a and 11 b.Unfortunately, performing this procedure with the use of conventionalbone screws is complex and involves a number of steps. First, thesurgeon reduces the fracture, and then drills a first hole 12 into thefirst bone segment 11 a, such that the first hole 12 has a diameter ₁equal to the major diameter of the screw 10. Next, the surgeon inserts adrill guide into the hole 12 and then drills a second hole 13 having adiameter ₂ that is equal to the minor diameter of the screw 10. Once thetwo holes are drilled, the bone is countersunk for the head of the screw10, the depth of the holes are measured to determine the length of screwneeded, and finally the screw is inserted and threads 14 of the screw 10are tightened into the second hole 13. FIG. 1B illustrates a procedurefor similarly attaching a bone plate 11 c to a bone segment 11 d using aconventional bone screw 10 with a fully threaded shaft.

SUMMARY

An expandable bone fixation assembly including an expandable fixationmember with an expandable shaft is provided. The expandable shaft has anaxial bore of a first inner diameter extending therethrough along a boreaxis that can be coincident with a central longitudinal axis of theshaft. The expandable shaft has a first external threaded sectionoriginating at the distal end of the shaft and extending towards theproximal end of the shaft along at least a portion of the shaft. Theexpandable fixation assembly also includes an expansion member having anelongate shaft with a mandrel at a distal end thereof. The elongateshaft is disposed within the bore of the expandable fixation member suchthat the mandrel is located at the distal end of the shaft. The mandrelhas a beveled surface and an outer dimension that is greater than thefirst inner diameter of the shaft. When the mandrel is biased throughthe expandable shaft, the mandrel causes the expandable shaft to bebiased radially outward and the threaded section of the shaft to engagewith surrounding structure, such as bone.

BRIEF DESCRIPTION OF THE DRAWINGS

The foregoing summary, as well as the following detailed description ofthe preferred embodiments of the application, will be better understoodwhen read in conjunction with the appended drawings. For the purposes ofillustrating the expandable fixation assembly systems and methods, thereare shown in the drawings preferred embodiments. It should beunderstood, however, that the instant application is not limited to theprecise arrangements and/or instrumentalities illustrated in thedrawings, in which:

FIG. 1A is a schematic illustration of a conventional bone screw with apartially threaded shaft joining two bone segments together;

FIG. 1B is a schematic illustration of a conventional bone screw with afully threaded shaft joining a bone plate and a bone segment together;

FIG. 2A is a sectional side elevation view of an expandable fixationmember that forms part of an expandable fixation assembly in accordancewith an embodiment;

FIG. 2B is a sectional side elevation view of the expandable fixationassembly illustrated in FIG. 2A, including an expansion member, prior toexpansion of the fixation member;

FIG. 2C is a sectional side elevation view of the expandable fixationassembly illustrated in FIG. 2B after expansion of the fixation member;

FIG. 2D is a sectional side elevation view of an expandable fixationassembly similar to that illustrated in FIGS. 2B-C, prior to expansionof the fixation member;

FIG. 2E is a sectional side elevation view of the expandable fixationassembly as illustrated in FIG. 2D after expansion of the fixationmember;

FIG. 2F is a sectional side elevation view of a portion of the fixationmember illustrated in FIG. 2A in accordance with another embodiment,prior to expansion of the fixation member;

FIG. 2G is a sectional side elevation view of a portion of the fixationmember illustrated in FIG. 2F, after expansion of the fixation member;

FIG. 2H is a schematic elevation view of a fixation member similar tothat illustrated in FIG. 2A, but showing an alternative externalanchoring geometry;

FIG. 2I is a schematic elevation view of an alternative expandablefixation assembly inserted between two bone segments separated by afracture;

FIG. 3A is a side elevation view of an expansion member in accordancewith an embodiment;

FIG. 3B is a side elevation view of the expansion member illustrated inFIG. 3A in accordance with an alternative embodiment;

FIG. 3C is a perspective view of an expandable fixation assembly inaccordance with an embodiment, prior to expansion of the expandablefixation member;

FIG. 3D is an end perspective view of the expandable fixation member ofthe expandable fixation assembly illustrated in FIG. 3C, prior toexpansion of the expandable fixation member;

FIG. 3E is a side elevation view of the expandable fixation assemblyillustrated in FIG. 3C, after partial expansion of the expandablefixation member;

FIG. 3F is an end perspective view of the expandable fixation member ofthe expandable fixation assembly illustrated in FIG. 3C, after expansionof the expandable fixation member;

FIG. 3G is a sectional side elevation view of the expandable fixationmember of the expandable fixation assembly illustrated in FIG. 3C inaccordance with an alternative embodiment, prior to expansion of thefixation member;

FIG. 3H is an end perspective view of the expandable fixation memberillustrated in FIG. 3G, prior to expansion of the expandable fixationmember;

FIG. 3I is a side elevation view of the expandable fixation memberillustrated in FIG. 3G, after expansion of the expandable fixationmember;

FIG. 3J is a sectional side elevation view of the expandable fixationmember of the expandable fixation assembly illustrated in FIG. 3C inaccordance with still another alternative embodiment, prior to expansionof the fixation member;

FIG. 3K is an end perspective view of the expandable fixation memberillustrated in FIG. 3J, prior to expansion of the expandable fixationmember;

FIG. 3L is a side elevation view of the expandable fixation memberillustrated in FIG. 3J, after expansion of the expandable fixationmember;

FIG. 4A shows an expandable fixation assembly including an expandablefixation member having self-drilling flutes constructed in accordancewith an embodiment;

FIG. 4B shows a self-drilling expandable fixation assembly including anexpandable fixation member having self-drilling flutes constructed inaccordance with an alternative embodiment;

FIG. 4C shows an anchoring geometry of the self-tapping flutes in thedirection of rearward movement with a conical runout of the threads;

FIG. 5 is a side elevation view of an expandable fixation assemblyhaving an expansion member inserted into a bore of the expandablefixation member;

FIG. 6A is a sectional side elevation view of the anchoring geometry ofan expandable fixation member in accordance with an embodiment;

FIG. 6B is a sectional side elevation view of the anchoring geometry ofan expandable fixation member in accordance with another embodiment;

FIG. 6C is a sectional side elevation view of an expandable fixationassembly including an alternative expansion member in accordance with anembodiment;

FIG. 7A is a sectional side elevation view of an expandable fixationmember having a head configured for angulation;

FIG. 7B is a sectional side elevation view of a portion of theexpandable fixation member illustrated in FIG. 7A;

FIG. 7C is a sectional side elevation view of the expandable fixationmember illustrated in FIG. 7A in accordance with an alternativeembodiment;

FIG. 7D is a sectional side elevation view of the expandable fixationmember illustrated in FIG. 7A in accordance with another alternativeembodiment;

FIG. 7E is a sectional side elevation view of the expandable fixationmember illustrated in FIG. 7A in accordance with still an alternativeembodiment;

FIG. 7F is a is a sectional side elevation view of a portion of theexpandable fixation member illustrated in FIG. 7E;

FIG. 8 is a sectional side elevation view of an expandable fixationmember having anchoring geometry configured to prevent screw looseningand/or migration in accordance with an embodiment;

FIGS. 9A-C are sectional side elevation views of an expandable fixationmember without a head in accordance with an embodiment;

FIG. 9D is a side elevation view of the expandable fixation memberillustrated in FIGS. 9A-C in accordance with an alternative embodiment;

FIG. 9E is a sectional side elevation view of the expandable fixationmember illustrated in FIG. 9D;

FIG. 9F is perspective view of an expandable intervertebral implantassembly in accordance with an embodiment;

FIG. 9G is a sectional front elevation view of the expandableintervertebral implant assembly illustrated in FIG. 9F, prior toexpansion of the expandable fixation members;

FIG. 9H is a sectional front elevation view of the expandableintervertebral implant assembly illustrated in FIG. 9F, after expansionof the expandable fixation members;

FIG. 9I is a sectional side elevation view of a pair of expandableintervertebral implant assemblies in accordance with an alternativeembodiment;

FIGS. 9J-O are elevation views of expandable fixation assemblies used inadjacent vertebral bodies in accordance with various spinal fixationembodiments;

FIG. 9P is a side elevation view of a pair of expandable fixationassemblies inserted into an interspinous spacer assembly in accordancewith an embodiment;

FIG. 9Q is a rear partially exploded elevation view of the interspinousspacer assembly illustrated in FIG. 9P;

FIG. 9R is a side elevation view of an expandable fixation assemblyinserted into an intervertebral implant in accordance with anembodiment;

FIG. 9S is a side elevation view of an expandable interspinous spacer inaccordance with an embodiment;

FIG. 9T is a side elevation view of an expandable vertebral stent inaccordance with an embodiment, prior to expansion of the stent;

FIG. 9U is a side elevation view of the expandable vertebral stentillustrated in FIG. 9T, after expansion of the stent;

FIGS. 9V-X are top elevation views of an expandable fixation memberinserted into a space within a lamina of a vertebral body and expanded,in accordance with an embodiment;

FIGS. 10A-B are sectional elevation views of expandable fixationassemblies that are partially expanded within respective bone segmentsin accordance with an embodiment;

FIG. 11A is a side elevation view of an expandable fixation memberhaving a shaft separated into a plurality of legs in accordance anembodiment;

FIG. 11B is a bottom elevation view of the expandable fixation memberillustrated in FIG. 11A;

FIG. 12A is a perspective view of an expandable cranial fixation memberin accordance with an embodiment;

FIG. 12B is a sectional elevation view of an expandable cranial fixationassembly including the expandable cranial fixation member illustrated inFIG. 12A, prior to expansion of the expandable cranial fixation member;

FIG. 12C is a sectional elevation view of the expandable cranialfixation assembly illustrated in FIG. 12B, after expansion of theexpandable cranial fixation member;

FIG. 12D is a sectional elevation view of the expandable cranialfixation assembly illustrated in FIG. 12B in accordance with analternative embodiment, prior to expansion of the expandable cranialfixation member;

FIG. 12E is a sectional elevation view of the expandable cranialfixation assembly illustrated in FIG. 12D, after expansion of theexpandable cranial fixation member;

FIG. 12F is a sectional elevation view of the expandable cranialfixation assembly illustrated in FIG. 12B in accordance with stillanother alternative embodiment, after expansion of the expandablecranial fixation member;

FIG. 13A is a sectional elevation view of an expandable cranial fixationassembly in accordance with an alternative embodiment, prior toexpansion of the expandable cranial fixation member;

FIG. 13B is a sectional elevation view of the expandable cranialfixation assembly illustrated in FIG. 13A, after expansion of theexpandable cranial fixation member;

FIG. 14A is a sectional elevation view of an expandable cranial fixationassembly in accordance with an alternative embodiment, prior toexpansion of the expandable cranial fixation member;

FIG. 14B is a sectional elevation view of the expandable cranialfixation assembly illustrated in FIG. 14A, after expansion of theexpandable cranial fixation member;

FIG. 14C is a bottom elevation view of the expandable cranial fixationassembly illustrated in FIG. 14A;

FIG. 14D is a sectional elevation view of the expandable cranialfixation assembly illustrated in FIG. 14A in accordance with analternative embodiment, prior to expansion of the expandable cranialfixation member;

FIG. 14E is a sectional elevation view of the expandable cranialfixation assembly illustrated in FIG. 14D, after expansion of theexpandable cranial fixation member;

FIG. 15A is a sectional elevation view of an expandable cranial fixationassembly in accordance with an alternative embodiment, prior toexpansion of the expandable cranial fixation member;

FIG. 15B is a sectional elevation view of the expandable cranialfixation assembly illustrated in FIG. 15A, after expansion of theexpandable cranial fixation member;

FIG. 15C is a sectional elevation view of the expandable cranialfixation assembly illustrated in FIG. 15A in accordance with analternative embodiment, after expansion of the expandable cranialfixation member;

FIG. 16A is a sectional elevation view of an expandable cranial fixationassembly in accordance with an alternative embodiment, prior toexpansion of the expandable cranial fixation member;

FIG. 16B is a sectional elevation view of the expandable cranialfixation assembly illustrated in FIG. 16A, after expansion of theexpandable cranial fixation member;

FIG. 16C is a perspective view of the expandable cranial fixationassembly illustrated in FIG. 16A;

FIG. 16D is a sectional elevation view of the expandable cranialfixation assembly illustrated in FIG. 16A in accordance with analternative embodiment, prior to expansion of the expandable cranialfixation member;

FIG. 16E is a sectional elevation view of the expandable cranialfixation assembly illustrated in FIG. 16D, after expansion of theexpandable cranial fixation member;

FIG. 16F is a sectional elevation view of the expandable cranialfixation assembly illustrated in FIG. 16A in accordance with analternative embodiment, prior to expansion of the expandable cranialfixation member;

FIG. 16G is a sectional elevation view of the expandable cranialfixation assembly illustrated in FIG. 16F, after expansion of theexpandable cranial fixation member;

FIG. 17A is a perspective view of an expandable cranial fixationassembly in accordance with an alternative embodiment;

FIG. 17B is a bottom elevation view of the expandable cranial fixationassembly illustrated in FIG. 17A disposed between bone segments;

FIG. 17C is a bottom elevation view of the expandable cranial fixationassembly illustrated in FIG. 17B, with the expandable cranial fixationmember rotated;

FIG. 17D is a sectional elevation view of the expandable cranialfixation assembly illustrated in FIG. 17A, prior to expansion of theexpandable cranial fixation member;

FIG. 17E is a sectional elevation view of the expandable cranialfixation assembly illustrated in FIG. 17D, after expansion of theexpandable cranial fixation member;

FIG. 17F is a sectional elevation view of the expandable cranialfixation assembly illustrated in FIG. 17A in accordance with analternative embodiment, prior to expansion of the expandable cranialfixation member;

FIG. 17G is a sectional elevation view of the expandable cranialfixation assembly illustrated in FIG. 17F, after expansion of theexpandable cranial fixation member;

FIG. 18A is an exploded perspective view of an expandable cranialfixation assembly in accordance with an alternative embodiment;

FIG. 18B is a sectional elevation view of the expandable cranialfixation assembly illustrated in FIG. 18A, prior to expansion of theexpandable cranial fixation member;

FIG. 18C is a sectional elevation view of the expandable cranialfixation assembly illustrated in FIG. 18B, after expansion of theexpandable cranial fixation member;

FIG. 18D is a sectional elevation view of the expandable cranialfixation assembly illustrated in FIG. 18A in accordance with analternative embodiment, prior to expansion of the expandable cranialfixation member;

FIG. 18E is a sectional elevation view of the expandable cranialfixation assembly illustrated in FIG. 18D, after expansion of theexpandable cranial fixation member;

FIG. 18F is a perspective view of a component of the expandable cranialfixation assembly illustrated in FIG. 18D;

FIG. 18G is a perspective view of the expandable cranial fixationassembly component illustrated in FIG. 18F in accordance with anotherembodiment;

FIG. 18H is a bottom elevation view of the expandable cranial fixationassembly component illustrated in FIG. 18G disposed between bonesegments;

FIG. 18I is a perspective view of the expandable cranial fixationassembly component illustrated in FIG. 18F in accordance with anotherembodiment;

FIG. 18J is a bottom elevation view of the expandable cranial fixationassembly component illustrated in FIG. 18H disposed between bonesegments;

FIG. 18K is a perspective view of the expandable cranial fixationassembly component illustrated in FIG. 18F in accordance with anotherembodiment;

FIG. 18L is a bottom elevation view of the expandable cranial fixationassembly component illustrated in FIG. 18K disposed between bonesegments;

FIG. 19A is a sectional front elevation view of an expandable cranialfixation assembly in accordance with an alternative embodiment, prior toexpansion of the expandable cranial fixation member;

FIG. 19B is a sectional front elevation view of the expandable cranialfixation assembly illustrated in FIG. 19A, after expansion of theexpandable cranial fixation member;

FIG. 19C is a sectional bottom elevation view of the expandable cranialfixation assembly illustrated in FIG. 19A, prior to expansion of theexpandable cranial fixation member;

FIG. 19D is a sectional front elevation view of the expandable cranialfixation assembly illustrated in FIG. 19A in accordance with analternative embodiment, prior to expansion of the expandable cranialfixation member;

FIG. 19E is a sectional front elevation view of the expandable cranialfixation assembly illustrated in FIG. 19D, after expansion of theexpandable cranial fixation member;

FIG. 19F is a sectional bottom elevation view of the expandable cranialfixation assembly illustrated in FIG. 19D, prior to expansion of theexpandable cranial fixation member;

FIG. 20A is a sectional elevation view of an expandable cranial fixationassembly in accordance with an alternative embodiment, prior toexpansion of the expandable cranial fixation member;

FIG. 20B is a sectional elevation view of the expandable cranialfixation assembly illustrated in FIG. 20A, after expansion of theexpandable cranial fixation member;

FIG. 21A is a sectional elevation view of an expandable cranial fixationassembly in accordance with an alternative embodiment, prior toexpansion of the expandable cranial fixation member;

FIG. 21B is a sectional elevation view of the expandable cranialfixation assembly illustrated in FIG. 21A, after expansion of theexpandable cranial fixation member;

DETAILED DESCRIPTION

For convenience, the same or equivalent elements in the variousembodiments illustrated in the drawings have been identified with thesame reference numerals. Certain terminology is used in the followingdescription for convenience only and is not limiting. The words “right”,“left”, “top” and “bottom” designate directions in the drawings to whichreference is made. The words “inwardly” and “outwardly” refer todirections toward and away from, respectively, the geometric center ofthe device and designated parts thereof. The words, “anterior”,“posterior”, “superior”, “inferior”, “lateral”, “medial”, “sagittal”,“axial”, “coronal,” “cranial,” “caudal” and related words and/or phrasesdesignate preferred positions and orientations in the human body towhich reference is made and are not meant to be limiting. The words“vertebral body” as used herein should be interpreted broadly to includeall the bones and bony structures found within and in the immediateproximity of the human spinal system, including but not limited to thosefound in the cervical region, the thoracic region, the lumbar region,and the sacral curve region. The words “bias,” “biased,” and “biasing”refer to causing the object being referred to, and designated partsthereof, to change position, for example by pushing, pulling, drawing,or otherwise applying force thereto. The terminology intended to benon-limiting includes the above-listed words, derivatives thereof andwords of similar import.

Referring now to FIGS. 2A-B, an expandable bone fixation assembly 20includes an anchoring region 37 that can include engagement structures,such as threads 36 or any alternative external geometry, configured tofasten an expandable fixation member 24 to one or more surroundingstructures that are to be joined, such as bone segments 22 a-b that havebeen separated by a fracture 21. It should be appreciated that referenceherein to threads includes a reference to any suitable external geometrycapable of fastening the expandable fixation member 24 to one or moresurrounding structures, such as bones and/or bone segments. Theexpandable fixation assembly 20 can alternatively fasten any desiredalternative structure to a bone and/or bone segment, for example anorthopedic screw, a bone anchor for soft tissue and/or ligamentfixation, a prosthesis, a nail, a rod, an external fixation member, andthe like.

While the mandible is one example of a bone whose fractured segments arejoinable with the expandable fixation assembly 20, the application ofthe expandable fixation assembly 20 is not intended to be limitedthereto, and is contemplated for use in conjunction with any suitablebones, bone segments, and/or in combination with bone on-lay or othertissue and osteosynthesis devices and/or materials, bone grafts, bonegraft substitutes such as synthetics, or bone substitutes. Two suchbones and/or bone segments are referred to herein as bone segments 22 aand 22 b. In the illustrated embodiment, the bone segment 22 a isreferred to as an outer bone segment and the bone segment 22 b isreferred to as an inner bone segment. While the fixation assembly 20 isillustrated as directly fastening the bone segments 22 a-b together, itshould be appreciated that the fixation assembly 20 can alternatively beused to fasten bone plates, grafts and/or other devices to an exteriorsurface of a bone and/or bone segment, and/or to fasten bone plates tobone grafts.

The expandable fixation assembly 20 includes the expandable fixationmember 24, which can be provided as a bone screw, a rivet screw, or thelike, and an expansion member 26 that is configured to expand thefixation member 24 so as to secure a portion of the fixation member 24that includes anchoring geometry, such as the threads 36 or any othersuitable exterior geometric structure, to surrounding structure, such asthe inner bone segment 22 b.

The fixation member 24, and other components of the various expandablefixation assemblies described herein, can be made from any suitablebiocompatible and/or resorbable materials and/or alloys (e.g., Ti alloy,TiCP, magnesium, stainless steel, plastics, polymers, etc.) whichprovide ductility for radial expansion as well as the stability towithstand the indication-specific, applied forces. The expansion member26 can be made of any suitable medical grade and/or biocompatiblematerial (e.g., instrument grade stainless steel or cobalt chrome) thatis sufficiently strong to expand the fixation member 24 and bebiocompatible. It is further desirable that the material allow for theexpansion member 26 to be fully drawn through the fixation member 24 andremoved therefrom. If a portion of the expansion member 26 is to be leftin the fixation member 24, like in a traditional rivet, then animplantable grade material would be desirable for the expansion member26. In one embodiment, the fixation member 24 is made from a titaniumalloy, and the expansion member 26 (specifically the mandrel 46described below) is made from a titanium alloy or cobalt chrome.

The fixation member 24, as depicted in FIG. 2A, includes a cannulated,or annular, shaft 28 that presents radially opposing inner and outersurfaces 25 and 27, respectively. The fixation member 24 is axiallyelongate along central longitudinal axis A-A. The shaft 28 defines aproximal end 30 that includes a head 32 and/or a second thread and/oranchoring geometry, an opposing distal end 34, and an intermediateportion 31 disposed between the proximal and distal ends 30 and 34. Theshaft 28 can be provided as a screw shaft, and the head 32 can beprovided as a screw head when the fixation member 24 is provided as abone screw. The shaft 28 defines one or more internal axial bores, forexample bores 35 and 35 a, formed along a bore axis that is coincidentwith the axis A-A, the bores extending through the head 32 and throughthe entirety of the shaft 28. The fixation member 24 further includesone or more anchoring regions 37, the anchoring regions 37 in radialalignment with the bore 35 and having anchoring geometry formed thereon,such as helical threads 36 that extend radially outward from the outersurface of the distal end 34 of the shaft 28. Of course the anchoringgeometry is not limited to threads, and can assume any suitable size andshape capable of biting into or otherwise engaging the bone segment 22 bonce the fixation member 24 has been radially expanded. The remainingportion of the outer surface of the shaft 28 is smooth, or unthreaded,though this portion could be fully or partially threaded and/orotherwise shaped to include any suitable alternative anchoring geometryas desired.

In the illustrated embodiment, the distal end 34 of the shaft 28 definesan inner diameter ID1 that is less than the inner diameter ID2 of boththe intermediate portion 31 and the proximal end 30 prior to radialexpansion of the fixation member 24, though it should be appreciatedthat the inner diameter ID1 can assume any desired relationship withrespect to the remainder of the fixation member 24 such that the distalend 34 is configured to radially expand in the manner described below.The outer diameter OD1 of the distal end 34 of the shaft 28 can be equalto, greater than, or less than, the outer diameter OD2 of the middleportion 31 and the proximal end 30 of the shaft 28 prior to radialexpansion of the fixation member 24. In the illustrated embodiment, theouter diameter OD1 is substantially equal to the outer diameter OD2.Furthermore, in the illustrated embodiment, the wall of the shaft 28 hasa thickness T that, at the distal end 34, can be greater than, lesserthan, or equivalent to the thickness T of the shaft 28 in the middleportion 31 or at the proximal end 30. It should be appreciated that theterm “diameter” as used herein applies to not only round objects in thetraditional sense, but is also intended to describe width dimensions(i.e., an “outer dimension”) for non-round objects, as measured in across-sectional fashion at the points of their greatest width.

Referring now to FIG. 2B, a bore 38 is drilled in the bone segments 22a-b prior to insertion of the fixation member 24. It should beappreciated that the terms “inner” and “outer” with respect to the axialdirection are used with respect to a direction into and out of the bore38, respectively. The bore 38 has a diameter, or cross-sectionaldimension, D1 that is equal to or greater than the outer diameter OD1 ofthe distal end 34 of the shaft 28 prior to expansion of the fixationmember 24. Thus, the fixation member 24 can be inserted axially into thebore 38 such that the head 32 abuts the outer surface of an outerstructure, such as a bone, a ligament, an osteosynthesis device such aplate or a hole therein, and the like. In the illustrated embodiment,the outer structure is bone segment 22 a. Prior to radial expansion ofthe fixation member 24, the fixation member 24 is loosely received inthe bore 38 such that the threads 36 are aligned with the inner bonesegment 22 b.

The expansion member 26 includes an axially elongate shaft 40 having aproximal end 42 and an opposing distal end 44. The shaft 40 can bedefined by a plurality of outer diameters along its length. The distalend 44 of the shaft 40 is coupled to a mandrel 46 that has an outerradial surface 48 that can be round, such that the mandrel 46 issubstantially spherical or ball-shaped. It should be appreciated thatthe mandrel 46 can be assume any alternative suitable shape such that adiameter or other outer dimension of the outer radial surface 48 isgreater than the inner diameter ID1 of the distal end 34 of the shaft 28and/or any other internal portion of the shaft 28 that is to beexpanded. In the illustrated embodiment, the outer radial surface 48 hasan outer dimension that is substantially equal to the inner diameter ID2of the middle portion 31 and the proximal end 30 of the shaft 28. Theouter radial surface 48 can further include a beveled surface 50 thatprovides a transitional interface between the distal end 44 of the shaft40 and the region of the outer radial surface 48 having the greatestdimension. The angle, or rake, of the beveled surface 50 may beconfigured to draw, or broach, material from the inner surface 25 of theshaft 28 as the mandrel is pulled therethrough. Generally, as the angleof the beveled surface with respect to the shaft 40 increases, anincreasing amount of material may be drawn through the shaft 82.Broaching of the shaft 28 by the mandrel 46 may act to decrease theamount of force needed to bias the mandrel 46 through the shaft 28.Broaching may also be achieved when the mandrel 46 is pushed into theshaft 28, as discussed in more detail below. The amount of material thatis broached, and thereby the amount of force required to bias themandrel 46 through the shaft 28, can be tailored by varyingcharacteristics of the fixation member 24 and/or the expansion member26, such as the material of the fixation member 24 and/or the expansionmember 26, the thickness T of the shaft 28, the rake/angle of thebeveled surface 50, and the like. The distal end 34 of the shaft 28 canbe configured with a complimentary beveled surface 52 that is configuredto engage the beveled surface 50 of the mandrel 46, as depicted in FIG.2B. One or more additional bevels can be formed within the shaft 28, forexample to act as diameter expansion and/or retraction transitions, as astop, a limitation, and the like.

Referring now also to FIG. 2C, it should be appreciated that theexpansion member 26 is typically pre-installed in the fixation member 24prior to inserting the fixation member 24 into the bore 38 of the bonesegments 22 a-b. In particular, the shaft 40 of the expansion member 26is received in the bore 35 of the fixation member 24, and the mandrel 46is disposed external to the shaft 28 at a location axially inward fromthe distal end 34. Once the fixation member 24 and the expansion member26 have been installed into the bore 38, a brace 56 can be placedagainst the outer surface of the head 32. The brace 56 can define aninner bore 58 that has a diameter or alternative cross-sectionaldimension that is greater than the outer diameters of the shaft 40 ofthe expansion member 26 and mandrel 46 such that the shaft 40 and themandrel 46 can be received in the bore 58. Once the brace 56 is placedin position, the expansion member 26 can be pulled through the shaft 28of the fixation member 24 while the brace 56 bears against the head 32to provide a reciprocal axial force against the force created by theexpansion member 26 as it is pulled through the shaft 28 of the fixationmember 24.

Referring now to FIGS. 2D and 2E, the illustrated fixation assembly 20is similar to that illustrated in FIGS. 2B-C, however the entire lengthof the shaft 28 of the fixation member 24 is expandable when theexpansion member 26 is drawn through the shaft 28. Only the anchoringregion 37 at the distal end 34 of the shaft 28 includes anchoringgeometry, such as the threads 36. The shaft 28 will only radially expandto the inner diameter of the bore 38 it is inserted into. This allows amandrel 46 having a non cylindrical shape, as described below withreference to FIGS. 3A-3L, to be drawn through the length of the shaft 28of the fixation member 24, thereby creating a drive recess in the shaft28. The drive recess allows engagement of a tool that is inserted intothe fixation member 24 for removal from, or tightening of, the fixationmember 24 with respect to the bore 38.

As the expansion member 26 is pulled into the distal end 34 of the shaft28 of the fixation member 24, the beveled surface 50 of the mandrel 46interferes with the beveled surface 52, thereby biasing the distal end34 of the shaft 28 radially outward. Thus, as the mandrel 46 is pulledthrough the distal end 34, the outer radial surface 48 of the mandrel 46biases the threads 36 into the surrounding structure of the inner bonesegment 22 b, thereby fastening the distal end 34 of the shaft 28 to thebone segment 22 b. Furthermore, the brace 56 applies a force to the head32 of the shaft 28 that can cause the head 32 to bend, or otherwisedeform, for example in a distal direction, into the outer surface 39 ofthe bone segment 22 a, thereby capturing the bone segment 22 a betweenthe head 32 of the shaft 28 and the bone segment 22 b. As a result, thebrace 56 could cause compressive forces F1 and F2 to be imparted ontothe bone segments 22 a-b, causing the bone segments 22 a-b to be drawntogether, thereby closing the fracture 21. Once the mandrel 46 hasadvanced past the distal end 34 of the shaft 28, it may be easily pulledthrough the middle portion 31 and the proximal end 30 and out of thefixation member 24. The brace 56 can be removed.

The contour of the outer surface of the fixation member 24 after it hasbeen expanded depends on the shape of the outer radial surface 48 of themandrel 46 of the expansion member 26 so that it is possible to changethe contour of the outer surface of the expanded shaft 28 and not onlythe bore 35 during the activation process. For example, if a mandrel 46with a hex shaped outer radial surface 48 is pulled through the shaft28, the mandrel 46 may cause one or more axial lobular ridges to beformed on the outer surface of the fixation member 24, the lobularridges corresponding with the intersection of the facets of the hexshaped outer radial surface 48 of the mandrel 46 and the inner surface25 of the fixation member 24.

Referring now to FIG. 2F-G, it should be appreciated that the shaft 28presents an anchoring geometry, such as the threads 36 and/or acombination of threaded and unthreaded sections within an expandableregion, or activation zone X_(U), of the shaft 28 that is configured toexpand as the mandrel 46 is pulled through the bore 35. As the length ofthe activation zone X_(U) increases, the axial force imparted onto thefixation member 24 by the mandrel 46 and the corresponding reciprocalaxial force imparted onto the head 32 by the brace 56 creates anincreasing compressive force onto the bone segments 22 a-b that closesthe fracture 21. It is possible to mitigate and/or to otherwisecompensate for the increased compressive force by tapering the thicknessT of the shaft 28 between the proximal and distal ends 30 and 34,respectively. As the mandrel 46 is pulled through the shaft 28, theportion of the shaft 28 within the activation zone X_(U) may becompressed axially, resulting in a shortened activated activation zoneX_(A), and a reduced overall length of the fixation member 24. Theamount of axial compression within the activation zone X_(U) can betailored by varying characteristics of the fixation assembly 20, forexample the material of the fixation member 24 and/or the expansionmember 26, the thickness T of the shaft 28, the geometry of theanchoring region 37, and the like. Once the resulting length of anactivated activation zone X_(A) is known, the overall length of thefixation member 24 can be designed so as to provide engagement by theexpanded anchoring region 37 at varying depths, for example within thebore 38. Thus, a kit can be provided including a plurality of fixationmembers 24 having different length activation zones X_(U) and/or overalllengths configured to provide varying levels of compressive forcesand/or anchoring region 37 engagement depths that may be suitable forparticular applications.

While the distal end 34 of the shaft 28 of the fixation member 24 caninclude an expandable region having external anchoring geometry, itshould be appreciated that the shaft 28 of the fixation member 24 canalternatively have an expandable region having external anchoringgeometry at any suitable location along its length, such that theexpandable region is configured to engage the surrounding bone in themanner described herein. For instance, referring to FIG. 2H, theanchoring geometry of the fixation member 24, in particular the threads36, extends along an entirety of the shaft 28 between the head 32 at theproximal end 30 and the distal end 34. The threads 36 can have aconstant outer diameter, or one or more sections of varying outerdiameters along the length of the shaft 28. As illustrated, the outerradial diameters of the threads 36 decrease in a direction from theproximal end 30 toward the distal end 34 of the shaft 28. Alternatively,the outer radial diameters of the threads 36 can increase in a directionfrom the proximal end 30 toward the distal end 34. Alternatively still,the outer radial diameters of the threads can increase or decrease fromthe proximal and/or distal ends 30 and 34 toward the middle portion 31of the shaft 28. The outer diameters of the threads 36 can vary in anycombination of the aforementioned.

Furthermore, while the inner diameter ID1 of the distal end 34 of theshaft 28 that includes anchoring geometry has been described as beingless than the inner diameter ID2 of the middle portion 31 and theproximal end 30 of the shaft 28, the inner diameter ID1 of the distalend 34 of the shaft 28 can alternatively be substantially equal to theinner diameter ID2 of the remainder of the shaft 28, or even slightlylarger than the inner diameter ID2 of the remainder of the shaft 28, solong as the outer dimension of the mandrel 46 is configured to bias aportion or all of the threads 36 of the anchoring region 37 radiallyoutward, thereby causing the expanded threads 36 to bite into and grip,or otherwise engage or mate with, the surrounding structure of the bonesegment 22 b, alone or in combination with the bone segment 22 a. It hasbeen found that a fixation member 24 of the type described hereinrequires a larger pull-out force to pull the fixation member 24 out ofthe bore 38 than an identically constructed screw of non-expandablenature.

As illustrated in FIG. 2I, the threads 36 can be configured to assist inthe compression of the bone segments 22 a-b toward each other, therebyreducing the fracture 21. In particular, a first set of threads 36 a atthe proximal end 30 of the shaft 28 can be aligned with the outer bonesegment 22 a, and a second set of threads 36 b at the distal end 34 ofthe shaft 28 can be aligned with the inner bone segment 22 b. To inducecompression between the bone segments 22 a-b, the threads 36 a and 36 bcan be configured with opposite thread angles with respect to each otherand/or can be configured with differing thread pitches. For instance,the threads 36 a that engage bone fragment 22 a can have one-half thepitch of the threads 36 b that engage the bone fragment 22 b, thethreads 36 a and 36 b can be configured with thread angles that areoriented away from the fracture line 21, or any combination thereof.Thus, as the threads 36 a-b are expanded radially outward in the mannerdescribed above, the thread angles and/or the pitches of the threads 36a-b cause the bone segments 22 a-b to become axially displaced towardthe fracture 21. While a pair of fixation members 24 is illustrated asbeing inserted into the bone segments 22 a-b, it should be appreciatedthat any desired number of fixation members 24 can be used. Furthermore,when the threads 36 a and 36 b are constructed with differing threadpitches, it is also possible to achieve axial displacement of the bonefragments 22 a and 22 b.

It should thus be appreciated that use of the expandable fixationassembly 20 reduces the number of steps associated with joining the bonesegments 22 a-b, with respect to conventional bone screws. For instance,a single hole (e.g., the bore 38) can be used to secure the fixationmember 24, thereby dispensing with the drill guide and the need to drilla second hole. Furthermore, because forces generated during pull throughof the expansion member 26 bias the head 32 of the shaft 28 against theouter surface of the surrounding structure, such as a bone or boneplate, the step of countersinking the bone is avoided. Thus, a methodfor installing the fixation member 24 includes the steps of reducing afracture (e.g., the fracture 21 between the bone segments 22 a and 22b), drilling a single through hole into the one or more bone segments,measuring the desired fixation member length, sliding the fixationmember 24 into the through hole, and expanding the fixation member 24with the expansion member 26. Furthermore, because the threads 36 can behelical, the fixation member 24 can be removed by rotating the fixationmember 24 in a manner consistent with conventional bone screws.

It should be appreciated that the embodiment of the fixation member 24illustrated in FIGS. 2A-C is an example embodiment, and that thefixation member 24 and/or the expandable fixation assembly 20 can beconstructed in accordance with numerous alternative embodiments, as willbe described in more detail below. The following alternative embodimentsare not intended to be exhaustive, and any additional or alternativeembodiments capable of allowing an expandable fixation member 24 tooperate in the manner described herein are intended to fall under thescope of the instant disclosure. It should be further appreciated thatfeatures and/or structures of the various embodiments illustrated anddescribed herein can be used in combination with other embodimentsillustrated and described herein.

Referring now to FIGS. 3A-3F, the mandrel 46 can impart a desiredgeometric shape to a portion or an entirety of the inner surface 25 ofthe shaft 28. In the illustrated embodiment, the outer radial surface 48of the mandrel 46 is illustrated as defining a hexagonal shape. Thus, asthe mandrel 46 is drawn through the shaft 28 of the fixation member 24in the manner described above (see FIG. 3C), the mandrel 46 imparts ahexagonal profile to the portion of the inner surface 25 that has aninner diameter or cross-sectional dimension that is smaller than theouter dimension of the outer surface 48. Accordingly, once the mandrel46 is removed from the fixation member 24, at least a portion of theinner surface 25 has a hexagonal cannulation, as illustrated in FIG. 3F.In an alternative embodiment of the mandrel 46 as illustrated in FIG.3B, one or more relief structures, for example grooves 49, can be formedwithin the outer radial surface 48 of the mandrel 46. The relief grooves49 reduce the surface area of the mandrel 46 that interferes with thebore 35 of the shaft 28 as the mandrel 46 is pulled therethrough,thereby reducing the amount of force required to pull the mandrel 46through the shaft 28.

The cannulation left by the mandrel 46, and more generally the bore 35of the shaft 28, can provide a medication port for the injection of adesired medication into the bore 38. The medication can, for instance,be injected with a standard syringe and without creating an additionalhole to provide access to the injection site. Additionally, the shaft 28of the fixation member 24 could have holes drilled normal to the outersurface through the wall and into the bore 35 of the shaft 28. Theseholes would allow the medication to be delivered into the surroundingbone. Additionally, a biodegradable or drug eluting polymer can beinserted into the bore 35 of the fixation member 24. The cannulationleft by the mandrel 46 can also be used in neurological applications,for example with intercranial pressure monitoring devices that may bedisposed within the cannulation, fluid monitoring devices, and the like.The cannulation can also serve as a drain port, for example in ashunting application

Furthermore, if it becomes desirable to remove the fixation member 24from the bone segments 22 a-b, a driving instrument, such as ascrewdriver having a hexagonal, or other polygonal engagement region asappropriate, can be inserted into the shaft 28 of the fixation member 24such that the hexagonal engagement region of the screwdriver mates withthe hexagonal cannulation of the fixation member 24. The screwdriver canthen be rotated in the usual manner, thereby causing the threads 36 toride along the surrounding bone, thereby backing the fixation member 24out of the bore 38. It should be appreciated from FIGS. 3C and 3E thatthe entire length of the shaft 28 can be threaded.

In an alternative embodiment of the fixation member 24 illustrated inFIGS. 3G-I, the bore 35 of the shaft 28 can be formed along a bore axisthat is offset with respect to the axis A-A, resulting in a non-uniformwall thickness of the shaft 28. Expanding a fixation member having anoffset bore 35 can result in an expanded fixation member 24 having acurved geometry. The curved geometry can produce a three-point contactload, for example at contact points 33, thereby increasing pulloutresistance of the expanded fixation member 24 with respect to the bore38. Alternatively, a fixation member 24 with an offset bore 35 and nothreads 36 can be used as a trauma plating pin. In such an application,non-threaded fixation members 24 with specific pullout resistances canbe manufactured. Additionally, a plurality of non-threaded fixationmembers 24 can be used in combination with a bone plate to prescribeopposing pin axial vectors.

In still another alternative embodiment of the fixation member 24illustrated in FIGS. 3J-L, the bore 35 of the shaft 28 can be formedalong a bore axis B-B that is offset and/or angled with respect to theaxis A-A, resulting in a non-uniform wall thickness of the shaft 28.Expanding a fixation member having an offset and/or angled bore 35 canresult in an expanded fixation member 24 having an “S” shaped geometry.The S shaped geometry can produce a four-point contact load, for exampleat contact points 33, thereby increasing pullout resistance of theexpanded fixation member 24 with respect to the bore 38. It should beappreciated that more or fewer than four contact points can result basedon the degree of offset and/or angulation of the bore axis B-B.Alternatively, a fixation member 24 with an offset and/or angled bore 35and no threads 36 can be used as a trauma plating pin. In such anapplication, non-threaded fixation members 24 with specific pulloutresistances can be manufactured. Additionally, a plurality ofnon-threaded fixation members 24 can be used in combination with a boneplate to prescribe opposing pin axial vectors.

Referring now to FIG. 4A, both the mandrel 46 and the fixation member 24can be self-drilling. In particular, the fixation member 24 and themandrel 46 can present axially outer cutting surfaces, such as cuttingflutes 51 and 53, respectively, at their axially leading edges. In thisembodiment the outer diameter, or outer dimension, of the mandrel 46 isless than that of the outer diameter OD1 of the threaded region of thefixation member 24 prior to expansion. During use, the mandrel 46 andthe fixation member 24 can be rotated as they are inserted into the bonesegments 22 a-b, such that the cutting flute 53 of the mandrel 46 cuts aportion of the bore 38 sufficient to allow the mandrel 46 to passthrough, and the cutting flute 51 of the fixation member 24 widens thebore 38, thereby allowing the shaft 28 to pass through to the positionillustrated in FIG. 2B. Thus, the bore 38 is drilled into the bonesegments 22 a-b simultaneously with the insertion of the fixation member24 and the mandrel 46. The mandrel 46 can then be pulled through theshaft 28 of the fixation member 24 in the manner described above tosecure the fixation member 24 to the bone segments 22 a-b.

In an alternative embodiment depicted in FIG. 4B, the cutting flutes 53of the mandrel 46 can have a diameter greater than the outer diametersOD 1 and/or OD2 of the shaft 28. In particular, the mandrel 46 caninclude a plurality of flexible legs 68 that flare away from each otherand are separated by an air gap 71. The cutting flutes 53 thereforedrill the bore 38 as the shaft 40 is rotated during insertion of thethreaded fixation assembly 20. The resulting bore 38 has a diameter D1greater than the outer diameters OD 1 and/or OD2 of the shaft 28 priorto expansion of the fixation member 24, thus the fixation member 24 isreceived loosely in the bore 38 created by the cutting surfaces 53. Asthe mandrel 46 is pulled through the bore 35 of the shaft 28, theflexible legs 68 collapse toward each other to define an outer diameter,or outer dimension, that is smaller than the bore 38 but larger than theinner diameter of the bore 35. Thus the mandrel 46 expands the shaft 28of the fixation member 24 as it is drawn through the shaft 28 in themanner described above. The expansion member 26 can include a threadedand/or form-locking structure at the proximal end of the shaft 40 thatassists in gripping the shaft 40 when pulling the mandrel 46 through thebore 35 of the shaft 28.

In another alternative embodiment, the fixation member 24 includes aplurality of self-tapping cutting flutes 70 disposed on the outersurface of the shaft 28 of the fixation member 24, for example inproximity to the distal end 34 of the shaft 28 and adjacent to theproximal end of the anchoring region 37. The cutting flutes 70 areconfigured to cut through surrounding bone during rotation of thefixation member 24 as the fixation member 24 moves in a backwarddirection (i.e., as the fixation member 24 is removed from the bore 38in the bone segments 22 a-b). It should be appreciated that the fixationmember 24 can receive a hexagonal or other polygonal cannulation in themanner described above, and/or the head 32 can include a suitable groovethat receives a screw driving instrument that can rotate the fixationmember 24. As depicted in FIG. 4C, the outer diameter of the cuttingflutes 70 can become progressively smaller in a direction from thedistal end 34 toward the proximal end 30 of the shaft 28, therebydefining a descending axial profile of cutting flutes. Accordingly, eachsuccessive cutting flute 70 incrementally removes a portion of thesurrounding bone, thereby ultimately widening the bore 38 to an amountat least as wide as the outer diameter OD2 of the threads 36, which issufficient to allow the remainder of the fixation member 24 to be easilypulled out of the bore 38 in the bone segments 22 a-b.

Referring now to FIG. 5, the expansion member 26 can be pushed into thebore 35 as opposed to being pulled through the bore 35 as describedabove. In the illustrated embodiment, the bore 35 is closed at thedistal end 34 of the shaft 28 at a location radially inward of thethreads 36. The portion of the bore 35 that is radially aligned with thethreads 36 presents an inner diameter smaller than the outer diameter,or outer dimension of the mandrel 46, such that inserting the mandrel 46into the bore 35 along the direction of Arrow B causes the shaft 28 toexpand in the manner described above. The method of expanding thefixation member 24 as illustrated in FIG. 5 includes the stepsidentified above with respect to FIGS. 2A-C, however instead ofinserting the fixation member 24 and the expansion member 26 into thebore 38 together, the fixation member 24 is inserted into the bore 38individually, and the mandrel 46 is then pushed axially inward into thebore 35. It should be appreciated that interference between the mandrel46 and the bore 35 biases the head 32 against the outer surface 39 ofthe bone segment 22 a, thereby reducing the fracture 21 between the bonesegments 22 a and 22 b, as the mandrel 46 is inserted into the bore 35.Once the fixation member 24 has expanded, the mandrel 46 can be easilyremoved from the fixation member 24. Alternatively, in accordance withthis or any other embodiment, once the fixation member 24 has beenexpanded as desired, the shaft 40 of the expansion member 26 can be cutsuch that the expansion member 26 can be left inside the shaft 28 of thefixation member 24 after expansion. Alternatively, in accordance withthis or any other embodiment, the shaft 40 of the expansion member 26can be manufactured in a predetermined length such that once thefixation member 24 has been expanded as desired, the expansion member 26will be contained within the shaft 28 of the fixation member 24 afterexpansion.

Furthermore, referring to FIG. 6A, the threaded portion of the shaft 28can include multiple threaded zones 36 c and 36 d that have at least onevarying thread characteristic. For instance, the threads 36 can havevarying depths at the corresponding zones 36 c and 36 d to allow forenhanced securement of the fixation member 24 to different layers ofbone. For example, deeper threads 36 are advantageous in a region of theshaft 28 that is secured in softer bone, such as cancellous bone. Thus,varying thread characteristics can be selected based on the propertiesof the bone region that is aligned with the expanding threads 36.

In the illustrated embodiment, threaded zone 36 c is configured to alignwith a cancellous bone portion, while the threaded zones 36 d aredisposed on both sides of the threaded zone 36 c and are configured toalign with cortex bone portions. Thus, the threads of the threaded zone36 c are spaced axially further apart, define a radial distance (orthread height) that is greater than the thread height of the threads inthe threaded zones 36 d, and are wider at their roots than the threadsin the threaded zones 36 d. However, because the inner diameter of theportion of the shaft 28 shaft that is radially aligned with the threadedzone 36 c is smaller than the diameter of the portions of the shaft 28that are radially aligned with the threaded zones 36 d, the outerdiameter of the threads 36 can be consistent across the threaded zones36 c and 36 d. Once the fixation member 24 is expanded, the threads ofthe threaded zone 36 c will be radially outwardly displaced with respectto the threads of the threaded zones 36 d. Alternatively, referring toFIG. 6B, the threaded zone 36 c, corresponding to cancellous bone, canbe devoid of threads, such that only the threads of the threaded zones36 d, associated with cortex bone, engage surrounding bone uponexpansion of the fixation member 24.

Referring now to FIG. 6C, the fixation member 24, having any desiredthread pattern and/or threaded sections, can be provided as a screw thatcan be inserted into the bone segments 22 a-b in a manner consistentwith conventional bone screws, and subsequently expanded if desired. Forinstance, the fixation member 24 can be provided with an expansionmember 26 disposed inside the bore 35, such that the distal end of themandrel 46 is either flush with the distal end 34 of the shaft 28, orrecessed in the bore 35. Accordingly, if the fixation member 24 is looseinside surrounding bone, or if another need arises to further secure thefixation member 24 inside the bore 38 formed in the bone, areciprocating brace can be placed against the outer surface of the head32. Once the brace is placed in position, the expansion member 26 can bepulled through the shaft 28 of the fixation member 24 while the brace 56bears against the head 32 to provide a reciprocal axial force againstthe force created by the expansion member 26 as it is pulled through theshaft 28 of the fixation member 24, thereby expanding the fixationmember 24 in the manner described above. Alternatively, the fixationmember 24 can be configured as illustrated in FIG. 5, such that themandrel 46 can be pushed into the shaft 28 of the fixation member 24 ifthe fixation member 24 is loose inside the bone segments 22 a-b, or itis otherwise desired to reinforce the structural integrity of the jointformed by the fixation member 24.

Referring now to FIGS. 7A-F, the fixation member 24 can be configuredfor angulation prior to expansion. For instance, the head 32 of thefixation member 24 can define a convex outer surface 72 configured tomate with a complementary concave inner surface 74 extending into a boneplate 62. Thus, engagement between the convex outer surface 72 and thenconcave inner surface 74 approximates a ball-and-socket joint thatallows for angulation of the fixation member 24 relative to the boneplate 62, whereby the axis A-A of the fixation member 24 can beangularly offset. The bore 35 of the shaft 28 can have a diameter orcross-sectional dimension at a location in radial alignment with thehead 32 that is less than the diameter of the outer surface 48 of themandrel 46. Accordingly, the convex outer surface 72 of the head 32 willradially expand into an interfering relationship with the concave innersurface 74 of the bone plate 62 when the mandrel 46 is pulled throughthe bore 35 of the shaft 28.

As shown in FIG. 7B, the concave inner surface 74 of the bone plate 62can include a plurality of anchoring geometries, such as threads 76,configured to bite into, or otherwise engage, the convex outer surface72 of the head 32 of the fixation member 24 in response to expansion ofthe head 32. In an alternative embodiment, the anchoring geometries cancomprise variable diameter, lobular, structures configured to deformagainst a plurality of concentric rings formed in the convex outersurface 72 of the head 32 or the concave inner surface 74 of the boneplate 62. It should be noted that the anchoring geometries can take theform of any other suitable engagement structure as desired. The head 32can be made from a material that yields more readily than the materialof the bone plate 62, and can include any suitable biocompatible and/orresorbable materials and/or alloys which offer a desired amount ofductility for the radial expansion as well as stability to withstand theindication-specific, applied forces. The bone plate 62 can be made fromany suitable material such as a stainless steel or titanium alloy. Thefixation members 24 can be made from a commercially pure titanium,softer grade of stainless steel, titanium alloy, polymer, and the like.Accordingly, the convex outer surface 72 can deform in response tocontact with the threads 76 of the concave inner surface 74, therebyenhancing the mating relationship between the bone plate 62 and the head32.

Alternatively, the concave inner surface 74 of the bone plate 62 can besmooth while the convex outer surface 72 of the head 32 has anchoringgeometries formed thereon, for example threads 76, such that the threads76 of the convex outer surface 72 bite into, or otherwise engage, theconcave inner surface 74 of the bone plate 62. Alternatively, both theconvex outer surface 72 of the head 32 and the concave inner surface 74of the bone plate 62 can be threaded or otherwise provided withanchoring geometries. Alternatively still, a bore 38 with a concavesurface can be formed in the bone segment 22 a, and the convex outersurface 72 of the head 32 can be threaded, such that the threads 76 ofthe convex outer surface 72 bite into, or otherwise engage, the concavesurface of the bone segment 22 a when the mandrel 46 is pulled throughthe head 32.

The embodiment depicted in FIGS. 7A-B creates an interference fitbetween the head 32 and the bone plate 62, thereby engaging the head 32of the fixation member 24 into a locked configuration within the boneplate 62. Accordingly, the fixation member 24 will no longer be able tomove independently of the bone plate 62, thereby preventing the fixationmember 24 from rotating about the axis A-A and backing out of the boneand/or bone plate. Furthermore, a single rigid construct is createdbetween the bone plate 62 and the fixation member 24, thus fixing thebone fragments 22 a-b rigidly. It should be appreciated that more axialrotation is allowed in defining an angle between the fixation member 24and the plate 62 than is allowed with respect to conventional bonescrews.

Additionally, because the locking occurs as the result of radialexpansion of the head 32, the locking forces created by the expansionare reproducible independent of any torque applied by the surgeon.Insertion torque can vary when fastening conventional bone screwswithout the use of a torque limiter. The fixation member 24 of theillustrated embodiment can achieve reproducible locking forces withoutthe use of a torque limiter. Furthermore, when using conventional bonescrews having a long length, the insertion torque required for the finaltightening of the screw can cause the screw to fail. In this regard, itshould be appreciated that the required insertion torque forconventional bone screws affects the locking stability and thus theoverall stability of the resulting construct. If too much torque is usedfor screw insertion, there is little left for locking torque. As aconsequence, too little locking torque may ultimately result in anunstable plate/screw mating interface and thus ultimately an unstablefracture construct. The fixation member 24 of the illustrated embodimentcan provide expansion forces, and forces applied by the fixation member24, that are independent of the length of the shaft 28 of the fixationmember 24.

In an alternative embodiment, as illustrated in FIG. 7C, one or moreaxial slots 41 can be formed within the head 32, the axial slots 41beginning in the proximal end of the head and extending into the head ina distal direction. The axial slots 41 can be configured to control thedegree of expansion of the head 32, while reducing the amount of forcethat must be applied to the shaft 40 of the expansion member 26 to pullthe mandrel 46 through the head 32. This configuration may be achievedby varying, for example, the number and/or length of the axial slots 41,the material the head 32 is manufactured from, and the like. Reducingthe amount of force that must be applied to the shaft 40 of theexpansion member 26 to pull the mandrel 46 through the head 32 canmitigate the likelihood that the shaft 40 and/or the mandrel 46 of theexpansion member breaking during the expansion process.

In another alternative embodiment, depicted in FIG. 7D, the shaft 28 ofthe fixation member 24 has a locking structure formed thereon, such asannular ridge 43 extending radially outward from the shaft 28 at theproximal end 30 of the shaft 28, just below the head 32. As the mandrel46 is pulled through the shaft 28, causing the shaft 28 to expandradially outward as described above, the annular ridge 43 expands andengages the lower surface of the bone plate 62. The expanded annularridge 43 provides further protection against backout of the fixationmember 24 from the bore 38, for example in addition to the lockingbetween the head 32 of the fixation member 24 and the bone plate 62described above.

In still another alternative embodiment, depicted in FIGS. 7E-F, thehead 32 of the fixation member 24 has a tapered, or variable diameter,bore formed therein. Varying the diameter of the bore 35 within the head32 allows control the expansion of the head 32 against the bone plate 62and/or the force required to pull the mandrel 46 through the head 32 ofthe fixation member 24. The inner diameter of the bore 35 in the head 32can be tapered to produce one or more distinct activation zones, such asactivation zones 32 a-c. In the illustrated embodiment, the firstactivation zone 32 a controls expansion of the shaft 28 of the fixationmember 24 within the surrounding bone of the bore 38. The secondactivation zone 32 b controls expansion of the convex outer surface 72of the head 32 against the concave inner surface 74 of the bone plate62. The third and final activation zone 32 c controls release of themandrel 46 as it is pulled through the proximal end of the head 32.

As shown in FIG. 8, the fixation member 24 can be threaded in a mannerthat is configured to prevent backout of the fixation member 24 from thebone segment 22. In particular, the head 32 of the fixation member 24can be disposed in a seat 65 of the bone plate 62 in the mannerdescribed above. For instance, the head 32 can threadedly engage theseat 65, or can present a smooth convex outer surface that nests withina smooth concave inner surface defined in the seat 65. A substantiallycylindrical or suitably alternatively shaped bore 80 can extend throughthe inner portion of the bone plate 62 at a location aligned with theseat 65. Accordingly, the shaft 28 of the fixation member 24 can extendthrough the bore 80 while the head 32 is disposed in the seat 65. Priorto expansion, the threads 36 can define an outer diameter that issubstantially equal to or smaller than the diameter of the bore 80 suchthat the shaft 28 can be inserted into the bore 80, through the boneplate 62, and into the bore 38 formed in the bone segment 22. One ormore, or a defined section, of the threads 36 located axially on theshaft 28 in close proximity to the inside surface of the bone plate 62,can be configured to act as locking threads 36, that is to expand to adiameter greater than the diameter of the bore 80 as the mandrel 46 ispulled through the shaft 28, thereby effectively locking the fixationmember 24 within the bore 38. Interference between the expanded lockingthreads 36 and the bone plate 62 prevents the fixation member 24 fromloosening (i.e., the fixation member 24 is prevented from unscrewingitself due to, for example, acting loads and/or micro movements of thebone segments). Accordingly, in some instances, a screwdriver may berequired to provide a predetermined torque in order to deform thelocking threads 36 in order to post-operatively remove the expandedfixation member 24.

Referring now to FIGS. 9A-C, the fixation member 24 can be providedwithout the head 32, such that the fixation member 24 only includes theshaft 28. Thus, the fixation member 24 of FIGS. 9A-C can be completelyembedded, for example as an implant, in the bone segment 22, and can beinwardly recessed with respect to the outer surface 39 of the bonesegment 22. The shaft 28 of the fixation member 24 can be inserted intothe bore 38, and the expansion member 26 can be inserted into the bore35 of the shaft 28 in the manner described above, or by rotating theshaft 40 of the expansion member 26. In particular, the outer surface ofthe shaft 40 of the expansion member 26 can have a plurality of threadsformed thereon, the threads configured to engage with complimentarythreads formed on the inner surface 25 of the shaft 28. The diameter, orother outer dimension, of the shaft 40 can be uniform throughout itslength. Alternatively the diameter, or other outer dimension, of theshaft 40 may be varied, for instance tapered, along one or moresections, or the entirety, of the length of the shaft 40. Thus, rotationof the shaft 40 relative to the fixation member 24 can cause theexpansion member 26 to be inserted, or driven, into the bore 35. Theexpansion member shaft 40 can be sized, for example via the diameter, orother outer dimension, to cause the shaft 28 of the fixation member 24to expand radially outward, thereby maintaining engagement of thethreads 36 with the surrounding bone of the bone segment 22. Expansionof the fixation member 24 reduces or prevents stress peaks in thebone/fixation member interface and generates a smoother intersectionbetween the material properties of the fixation member 24 and the weakerproperties of the surrounding bone of the bone segment 22. In an exampleembodiment, the headless fixation member 24 depicted in FIGS. 9A-C couldbe used in an expandable knee implant assembly.

In an alternative embodiment depicted in FIGS. 9D-E, the fixation member24 can alternatively be used as a spacer between two adjacent bones 22a-b, for example to maintain a desired spacing therebetween. The outersurface of the intermediate portion 31 of the shaft 28 has a pluralityof helical threads 36 extending outwardly therefrom, and the outersurface of the proximal and distal ends 30 and 34 of the shaft 28 aresmooth. The inner diameter of the bore 35 in the intermediate portion 31of the shaft 28 is smaller than the inner diameter of the bore at theproximal and distal ends 30 and 34 of the shaft, such that the outsidediameter of the shaft is uniform between the proximal and distal ends 30and 34, and such that only the intermediate portion 31 of the shaft 28is expanded when the mandrel 46 is pulled through the shaft 28. As themandrel 46 is pulled through the shaft 28 in the manner described above,the intermediate portion 31 of the shaft expands radially outward,causing the threads 36 to engage the adjacent bone and to secure theposition of the fixation member 24 between the bone segments 22 a-b, andthereby the spacing between the bone segments 22 a-b.

In still another alternative embodiment depicted in FIGS. 9F-H, a pairof expandable fixation assemblies 20 are used in combination with anintervertebral implant 156 in an expandable intervertebral implantassembly 157. The intervertebral implant 156 includes an implant body158 having a generally rectangular shape defining opposing proximal anddistal ends 158 a and 158 b, and opposing upper and lower surface 158 cand 158 d. It should be appreciated that the rectangular shape of theimplant body 158 is merely an example implant body geometry, any thatother implant body geometry may be used as desired, for example asanatomy in a target intervertebral space may dictate. The upper andlower surfaces 158 c and 158 d may be smooth, may have gripping featuressuch as teeth, spikes, or similar structures formed thereon andconfigured to facilitate gripping engagement between the upper and lowersurfaces 158 c and 158 d and the end plates of adjacent vertebralbodies, or may have discrete smooth and gripping portions. The body canfurther include an optional central bore 164 configured, for example, tobe filled with bone growth inducing substances to allow bony ingrowthand to assist in fusion between the intervertebral implant 156 andadjacent vertebral bodies.

The implant body 158 can have one or more fixation assembly bores formedtherein, the bores having an inner diameter larger than the outerdiameter of one or more expandable fixation assemblies 20 that aredisposed within the bores. In the illustrated embodiment, a pair ofbores 160 are formed in the proximal end 158 a of the implant body 158,extending in a rearward direction along a pair of bore axes S toward thedistal end 158 b. The implant body 158 can further have one or moreopenings in the outer surface of the implant body that are configured toallow bone engagement structures to protrude from the implant body 158and engage surrounding structure, such as the end plates of adjacentvertebral bodies. In the illustrated embodiment, a pair of verticalslots 162 are formed through the implant body 158 and the bores 160between the upper and lower surfaces 158 c and 158 d, the slots 162aligned lengthwise with the shaft axes S. The expandable fixationassemblies 20 are disposed within respective bores 160.

One or more engagement structures, such as engagement blocks 166, can bedisposed within the implant body 158, the engagement block 166configured to be disposed on opposing sides of the expandable implantassemblies 20, between the fixation members 24 and the upper and lowersurfaces 158 c and 158 d of the implant body 158, such that when thefixation members 24 are expanded, the engagement blocks 166 are biasedtoward respective upper and lower surfaces 158 c and 158 d of theimplant body 158, with at least a portion of the engagement blocks 166protruding from the implant body 158, for example through the slots 162,and engaging surrounding structure. It should be appreciated that thepositioning of the slots 162 in the illustrated embodiment is merely anexample, and that more or fewer slots, or other geometric openings, canbe positioned in any suitable location on the surface of the implantbody 158.

The engagement blocks 166 have opposing fixation member facing surfaces,and bone facing surfaces, the bone facing surfaces having one or morebone engagement structures formed thereon, for example a plurality ofteeth 168. In the illustrated embodiment The engagement blocks 166 arecarried within the implant body 158, between the expandable fixationassemblies 20 and the upper and lower surfaces 158 c and 158 d of theimplant body 158, as described above. The engagement blocks 166 areconfigured to be of such a thickness that before the fixation members 24are expanded, the teeth 168 are contained within the implant body 158.In alternative embodiments, the engagement blocks 166 can be omitted,such that bone engagement structures formed on the outer surfaces of thefixation members 24 engage the surrounding structure directly, asdescribed in more detail below.

During use, the expandable intervertebral implant assembly 157 isdisposed within an intervertebral space, for example between twoadjacent vertebral bodies V, as depicted in FIG. 9G. When the implant156 is positioned as desired, the mandrels 46 can be pulled through theshafts 28 of the respective fixation members 24, causing the shafts 28of the fixation members 24 to expand radially outward, thereby biasingthe engagement blocks 166 in respective cranial and caudal directions,such that the teeth of the engagement blocks protrude through theopenings of the slots 162 and engage respective endplates of theadjacent vertebral bodies V as illustrated in FIG. 9H, thereby fixingthe expandable intervertebral implant assembly 157 in position withinthe intervertebral space. If it is desirable to remove the implant 156after insertion, a screw driving tool can be inserted into the expandedbores 35 of the fixation members 24 as described above, allowing thefixation members 24 to be removed from the bores 160 of the implant body158. Once the fixation members 24 are removed from the implant 156, theengagement blocks 166 can return to their pre-insertion configuration,such that the teeth 168 no longer engage the adjacent vertebral bodiesV. The implant can then be easily removed.

In still another alternative embodiment depicted in FIG. 9I, a pair ofexpandable intervertebral implant assemblies 157 are provided as bonespacers disposed in corresponding voids 170 between adjacent bonesand/or bone segments 22 a-c. In the illustrated embodiment, the slots162 of the previously discussed embodiment are omitted, and the outersurfaces of the implants 156 have bone engagement structures formedthereon, for example teeth 158. During use, the implants 156 aredisposed within the voids 170 between the bones and/or bone segments 22a-c and positioned as desired. As the mandrels 46 are pulled though theshafts 28 of the fixation members 24, the shafts 28 of the fixationmembers 24 expand radially outward against the inner surfaces of thebores 160, causing the bodies 158 of the implants 156 to expand withinthe voids 170, and in turn causing the teeth 168 to engage with theoutside surfaces of the bones and/or bone segments 22 a-c, therebyfixing the implants 156 in position within the voids 170. In order toensure that the implant bodies 158 retain their expanded geometries, theshafts 40 of the expansion members 26 can be cut as described above,such that the mandrels 46 are retained within the bores 35 of thefixation members 24. It should be appreciated that fixation members 24having differing shaft thickness T and/or anchoring regions 37 can beused with a single implant body configuration, for example to achievevarying degrees of expansion of the implant body 158 as desired.Furthermore, the implant body itself can be configured as the fixationmember 24, such that the mandrels 46 are pulled through bores 35 formedwithin the implant body 158/fixation member 24, causing direct expansionthereof.

Referring now to FIGS. 9J-O, the expandable fixation assemblies 20described herein can be used in spinal fixation procedures in place oftypical fasteners used in such procedures such as bone screws, pediclescrews, and the like. For example expandable fixation assemblies 20 canbe used in translaminar fixation as depicted in FIG. 9J, facet fixationas depicted in FIG. 9K, and pedicle/rod fixation constructs as depictedin FIG. 9L. Use of the expandable fixation assemblies 20 disclosedherein is desirable for deep recess procedures such as these because,unlike typical fasteners that can fall off the end of the insertioninstrument, the expansion member 26 prevents the fixation member 24 fromsimilarly falling off within the surgical site.

Referring now to FIGS. 9P-X, the expandable fixation assemblies 20described herein can be used to anchor vertebral implants and/orspacers. For example, as depicted in FIGS. 9P-Q, a pair of fixationassemblies 20 are used to anchor an interspinous spacer 172 betweenadjacent spinous processes SP. The fixation members 24 may be insertedthrough the bores 80 in the bone plates 62 coupled to the spacer 172,and through pre-drilled bores 38 in the spinous processes SP. Themandrels 46 can then be pulled through the fixation members 24 asdescribed above, thereby fixing the interspinous spacer 172 in placebetween the spinous processes SP. The inner surfaces of the bores 80 maybe smooth, or may have anchoring geometries, such as threads 76, formedthereon, the anchoring geometries configured to engage complimentaryengagement structures on the fixation members 24, such as threads 36.

In an alternative embodiment depicted in FIG. 9R, an expandable fixationassembly 20 is used to anchor an intervertebral implant 174 to anadjacent vertebral body V. The fixation member 24 is inserted through abore 177 in the body 176 of the implant 174 and into a pre-drilled bore38 in the adjacent vertebral body V. The mandrel 46 can then be pulledthrough the fixation member 24 as described above, thereby fixing theintervertebral implant 174 in place within the intervertebral space.

In still another alternative embodiment depicted in FIG. 9S, anexpandable fixation member 24 is disposed within the body 178 of aninterspinous spacer 180. The interspinous spacer 180 disposed within aninterspinous space between two adjacent spinous processes SP. When themandrel 46 is pulled through the shaft 28 of the fixation member 24, theshaft 28 expands radially outward, thereby expanding the body 178 of theinterspinous spacer 180 within the interspinous space.

In yet another alternative embodiment depicted in FIGS. 9T-U, thefixation member 24 of an expandable fixation assembly 20 can beconfigured for used as a vertebral body stent. The expandable fixationassembly is disposed into a pre-drilled bore 38 within a vertebral bodyV. When the mandrel 46 is pulled through the shaft 28, the fixationmember 24 expands radially outward, thereby stenting the vertebral bodyV.

In still another alternative embodiment depicted in FIGS. 9V-X, anexpandable fixation assembly 20 can be used in a laminoplasty procedure.After the desired amount of material has been removed from the targetlamina L, thereby creating a bore 38 in the lamina L, the fixationmember 24 is disposed within the lamina L. As the mandrel 46 is pulledthrough the shaft 28, the fixation member 24 expands radially outward,thereby biasing the adjacent bone segments 22 a-b of the lamina Loutward, expanding the foramen, and causing the threads 36 on the outersurface of the shaft 28 of the fixation member 24 to engage with thesurfaces of the adjacent bone segments 22 a-b of the lamina L. It shouldbe appreciated that the fixation member 24 and/or the expandablefixation assembly 20 can replace typical bone screws or othertraditional anchors in any suitable surgical procedure as desired.

Referring now to FIGS. 10A-B, the fixation member 24 can be used for thepurposes of grabbing and manipulating bone segments 22 a-c, for instanceof a mandible, into desired positions with respect to one or moreadjacent bones or bone segments. In particular, the bore 38 can bedrilled into the bone segment 22 a, the distal end 34 of the shaft 28can be inserted into the bore 38, and the mandrel 46 can be pulled intoradial alignment with at least a portion of the expandable threads 36such that the aligned threads 36 expand into the bone segment 22 a. Theshaft 40 of the expansion member 26 can then be used as a joystick, andcan be manually maneuvered to manipulate the position of the bonesegment 22 a into a desired position. The bone segment 22 a can then befastened to the one or more adjacent bones or bone segments as desired.Once the bone segment 22 a is securely fastened in place, a rotationalforce can be applied to the shaft 40 of the expansion member 26 in orderto back the fixation member 24 out of the bore 38 for removal.Alternatively, the expansion member 26 can be pulled all the way throughthe shaft 28 so the fixation member 24 remains in the bore 38, forexample if it is being used to hold a bone plate in place. These samesteps can be applied to position the bone segments 22 b-c for fixation.Fractures to which this method can be particularly applicable includebut are not limited to subcondylar fractures, frontal sinus fractures,and the like.

Referring now to FIGS. 11A-B, the shaft 28 of the fixation member 24 canbe axially divided into a plurality of circumferentially separated shaftsegments, or legs, 28 a-d. Thus, less force is required to pull themandrel 46 through the shaft 28 since the mandrel encounters lessresistance from the segmented shaft than it does from thecircumferentially solid shaft 28 described above. The proximal end 30 ofthe fixation member 24 has a closed profile, such that the legs 28 a-dare joined together at the proximal end 30 of the shaft 28. Accordingly,as the mandrel 46 is pulled into the bore 35 at the distal end 34 of theshaft 28, the outer surface of the mandrel 46 interferes with the innersurfaces of the legs 24 a-d, causing the legs 28 a-d to deflect radiallyoutward, thereby causing the threads 36 on the outside surfaces of thelegs 28 a-d to bite into, or otherwise engage, the surrounding bone inthe manner described above. Furthermore, after expansion, the shaft 40of the expansion member 26 can be cut at a location aligned with, orrecessed in, the proximal end 30 of the shaft, such that the mandrel 46remains disposed in the bore 35 at a location aligned with the expandedthreads 36, so as to maintain the biasing force of the mandrel 46against the legs 28 a-d, and thereby to maintain the engagement of thethreads 36 with the surrounding bone.

Referring now to FIGS. 12A-F, generally speaking, expandable fixationassemblies can be configured to secure two or more bone segments withrespect to each other. For example, expandable fixation assemblies canbe configured for use in cranial fixation procedures, for instance asexpandable cranial fixation assemblies including expandable cranialfixation members configured as expandable cranial clamps for use insecuring bone flaps in craniotomies. In general, expandable cranialfixation members such as cranial clamps can be configured using avariety of expandable fixation member bodies, as described in moredetail below. In particular, as illustrated in FIGS. 12A-C, anexpandable cranial fixation assembly 82 includes an expandable fixationmember such as cranial clamp 84, and an expansion member 26. The cranialclamp 84 includes an expandable fixation member body, such as discshaped body 86, the body 86 having a central aperture 86 a with an innerdiameter ID3 formed therethrough. The body 86 has an upper surface 86 b,and an opposing lower surface 86 c. The upper and lower surfaces 86 band 86 c, respectively, can be configured to conform to a particularanatomical region, for example a particular area on the outer surface ofthe skull, so as to maximize contact between the lower surface 86 c andunderlying bone segments 88 a and 88 b, while simultaneously minimizingthe profile of the upper surface 86 b with respect to the outer surfaceof the bone segments 88 a and 88 b. In the illustrated embodiment, theupper surface 86 b is convex, and the opposing lower surface 86 c isconcave. In an alternative embodiment, one or more of the upper andlower surfaces 86 b and 86 c can be flat. It should be noted that anyalternative body geometry, surface profile, and/or aperture locationscould be used as desired.

The body 82 of the cranial clamp 84 further includes a ductilecannulated shaft 86 d having a proximal end 86 e and an opposing distalend 86 f, the shaft 86 d extending in a downward, or caudal, directionfrom the proximal end 86 e at the lower surface 86 c along a centralshaft axis S, the thickness of the shaft 86 d defined by an outerdiameter OD3 that is greater than, and an inner diameter ID4 that issmaller than, the inner diameter ID3 of the aperture 86 a. Although theillustrated embodiment depicts the shaft 86 d as having a uniformthickness between the proximal and distal ends 86 e and 86 f, it shouldbe appreciated that the outer diameter OD3 and/or the inner diameter ID4can be tapered, or otherwise varied, along one or more sections, oralong the entirety, of the length of the shaft 86 d between the proximaland distal ends 86 e and 86 f, respectively. The inner diameter ID4 mayalso be slightly smaller than the outer dimension of the outer surface48 of the mandrel 46. The shaft 86 d is divided into a plurality ofradially separated shaft segments, or legs, 90 a-d, for example by axialslots 92 a-d. The slots begin at the distal end 86 f of the shaft 86 dand extend in an upward, or cranial, direction into the shaft,terminating in a circumferentially solid portion 86 g of the shaft 86 d.Although the illustrated embodiment has four axial slots defining fourcorresponding legs, any corresponding number of axial slots may be usedto define a desired number of legs.

During use, the cranial fixation assembly 82 can be used to secure bonesegments 88 a and 88 b, for example a bone flap that is being rejoinedto a patient's skull. A plurality of cranial fixation assemblies 82 maybe disposed within the gap between the bone flap and the skull atvarious locations along the perimeter of the bone flap as desired. Oncea respective cranial fixation assembly 82 is disposed in a desiredlocation, a downward, or caudal, biasing force is applied to the uppersurface 86 b of the cranial clamp 84, for example by an insertioninstrument. An upward, or cranial, force is applied to the elongateshaft 40 of the expansion member 26, in the direction of arrow M,thereby drawing the mandrel 46 into the distal end 86 f of the shaft 86d. As the mandrel 46 enters the distal end 86 f of the shaft 86 d, theouter surface 48 of the mandrel 46 interferes with the distal ends ofthe legs 90 a-d, causing the legs to deflect outwardly from theadvancing mandrel 46. The degree of curvature exhibited by the legs 90a-d may result from, for example, the radial thickness of the legs asdefined by the outer and inner diameters OD3 and ID4 of the shaft 86 d,the difference between the inner diameter ID4 of the shaft 86 d and theouter dimension of the outer surface 48 of the mandrel 46, the materialof manufacture of the cranial clamp 84, the speed with which the mandrel46 is advanced within the shaft 86 d, and other such factors. Thedeformation characteristics of the legs 90 a-d may be tuned viavariation of one or more of the above, and/or similar factors.

As the mandrel continues to travel upward within the shaft 86 d, itleaves the portion of the shaft 86 d including the legs 90 a-d andenters the circumferentially solid portion 86 g of the shaft 86 d beyondthe proximal ends of the slots 92 a-d. The curvature imparted to thelegs 90 a-d may cause the outer surface of one or more of the legs 90a-d to engage the inner surface of the bone segments 88 a and 88 b inproximity to the edges 88 c, thereby drawing the lower surface 86 c ofthe cranial implant 84 against the outer surfaces of the bone segments88 a and 88 b, and imparting a compressive, or clamping, force onto thesurfaces of the bone segments 88 a and 88 b disposed between the lowersurface 86 c of the cranial implant 84 and the outer surface of the legs90 a-d.

As the mandrel 46 passes through the circumferentially solid portion 86g of the shaft 86 d and out of the aperture 86 a, the shaft 86 d mayexpand radially outward, thereby augmenting the outer and innerdiameters OD3 and ID4, respectively. The outer diameter OD3 may beaugmented such that the outer surface of the circumferentially solidportion 86 g of the shaft 86 d engages at least a portion of the edges88 c of the bone segments 88 a and 88 b, inducing a friction fit of thecranial clamp 84 within the gap between the bone segments 88 a and 88 b.Additionally, the inner surface of the shaft 86 d and/or the aperture 86a may deform to conform to the shape of the outer surface 48 of themandrel 46.

In an alternative embodiment as depicted in FIGS. 12D-E, the cranialfixation assembly 82 further includes a retention structure, for examplea retaining plug 91. The retaining plug 91 is configured to ensureretention of the cranial clamp 84 between the bone segments 88 a and 88b after the mandrel 46 has been pulled through the shaft 86 d. Theretaining plug 91 has a generally conical shaped body 93 defined betweena proximal end 93 a and an opposing distal end 93 b. The diameter of thebody 93 at the proximal end 93 a is slightly smaller than the innerdiameter ID4 of the shaft 86 d. The diameter of the body 93 increasesgradually between the proximal end 93 a and the distal end 93 b. Theretaining plug 91 has an axial bore 93 c formed therethrough, the axialbore 93 a having an inner diameter that is slightly smaller than theouter dimension of the outer surface 48 of the mandrel 46. The innerdiameter ID4 of the shaft 86 d may be enlarged so that the retainingplug 91 can be received in the shaft 86 d as the mandrel 46 is pulledtherethrough. Additionally, the distal ends of the legs 90 a-d can betapered, flared, or otherwise configured to facilitate engagementbetween the legs 90 a-d and the outer surface of the retaining plug 91as it enters the shaft 86 d. The retaining plug 91 can be inserted ontothe expansion member 26 and disposed within the cranial clamp 84 beforethe cranial fixation assembly 82 is disposed into a surgical site.

During use, as the mandrel 46 enters the distal end of the axial bore 93c of the retaining plug 91, the outer surface 48 of the mandrel 46interferes with the inner surface of the axial bore 93 c, causing theretaining plug 91 to be drawn upward into the shaft 86 d. As theretaining plug 91 advances into the shaft 86 d, the outer surface of theretaining plug interferes with the distal ends of the legs 90 a-d,causing the legs to deflect outwardly from the advancing retaining plug91 and to engage the inner surface of the bone segments 88 a and 88 b inproximity to the edges 88 c, thereby resulting in a clamping forceapplied to the bone segments 88 a and 88 b as described above. Theadvancing retaining plug 91 can also cause radial expansion of the shaft86 d, thereby causing the outer surfaces of one or more of the legs 90a-d to engage the edges 88 c of the bone segments 88 a and 88 b, therebyinducing a friction fit of the cranial clamp 84 within the gap betweenthe bone segments 88 a and 88 b. As the retaining plug 91 enters thecircumferentially solid portion 86 g of the shaft 86 d, the forcesbetween the retaining plug and the legs 90 a-d can activate the legs 90a-d into a locked configuration.

In still another alternative embodiment depicted in FIG. 12F, themandrel 46 can be configured to act as a retaining plug. For example,the mandrel 46 could have a narrow, or “necked in,” section 40 a, thediameter, or other outer dimension of the narrow section 40 a configuredto break when a desired level of biasing stress is reached in the shaft40. In the illustrated embodiment, as the mandrel 46 is pulled into thecircumferentially solid portion 86 g of the shaft 86 d, the biasingstress would cause the shaft 40 of the expansion member 26 to break atthe narrow section 40 a, thereby leaving the mandrel 46 disposed withinthe shaft 86 d, to act as a retaining plug to activate the legs 90 a-dinto a locked configuration.

Referring now to FIGS. 13A-B, the cranial fixation assembly 82 and thecranial clamp 84 are illustrated in accordance with another embodiment.In the illustrated embodiment, the axial slots 92 a-d extend along theentire length of the shaft 86 d between the proximal and distal ends 86e and 86 f, respectively. The thickness of the legs 90 a-d, as definedby the outer and inner diameters OD3 and ID4 of the shaft 86 d, can bevaried over at least of a portion of the length of the shaft 86 dbetween the proximal and distal ends 86 e and 86 f thereof. Varying thethickness of the legs 90 a-d may determine the deformation behavior ofthe legs 90 a-d as the mandrel 46 is advanced in the shaft 86 d, asexplained in more detail below. In the illustrated embodiment, thethickness of the legs 90 a-b is uniform throughout a first intermediatesection 96 a of the length to the shaft 86 d that begins at the distalend 86 f of the shaft and extends in an upward direction into the shaft86 d. In a second intermediate section 96 b, extending between the endof the first intermediate section 96 a and the proximal end 86 e of theshaft 86, the thickness of the legs 90 a-d gradually increases, and isgreatest at the proximal end 86 e of the shaft 86 d. Additionally, thedistal ends of the legs 90 a-d include bone engagement structures, suchas feet 94 a-d, formed at the distal ends thereof, the feet configuredto engage the bone segments 88 a and 88 b.

During use, the illustrated embodiment of the cranial fixation assembly82 can be used to secure bone segments 88 a and 88 b. Once a respectivecranial fixation assembly 82 is disposed in a desired location, adownward, or caudal, biasing force is applied to the upper surface 86 bof the cranial clamp 84, for example by an insertion instrument. Anupward, or cranial, force is applied to the elongate shaft 40 of theexpansion member 26, thereby drawing the mandrel 46 into the distal end86 f of the shaft 86 d. As the mandrel 46 enters the distal end 86 f ofthe shaft 86 d and advances into the first intermediate portion 96 a,the outer surface 48 of the mandrel 46 interferes with the distal endsof the legs 90 a-d, causing the legs to deflect outwardly from theadvancing mandrel 46. Furthermore, the deflection of the legs 90 a-d cancause the upper surfaces of the feet 94 b and 94 d to engage with thelower, or inner, surfaces of the bone segments 88 a and 88 b, therebydrawing the lower surface 86 c of the cranial implant 84 against theouter surfaces of the bone segments 88 a and 88 b, and imparting acompressive, or clamping, force onto the surfaces of the bone segments88 a and 88 b disposed between the lower surface 86 c of the cranialimplant 84 and the upper surfaces of the feet 94 b and 94 d.

As the mandrel 46 advances further into the shaft 86 d, and into thesecond intermediate portion 96 b, the legs 90 a-d may continue todeflect from the mandrel 46, and the increasing thickness of the legs 90a-d in the second intermediate portion 96 b may cause the shaft 86 d toexpand radially outward as described above, causing the outer surfacesof one or more of the legs 90 a-d to engage the edges 88 c of the bonesegments 88 a and 88 b, thereby inducing a friction fit of the cranialclamp 84 within the gap between the bone segments 88 a and 88 b. Itshould be appreciated that while the illustrated embodiment depictsengagement by only the feet 94 b and 94 d, the feet 94 a-d can be soconfigured, and the cranial fixation assembly 82 can be so orientedduring insertion, that any combination of one or more, including all, ofthe feet 94 a-d engage the lower surfaces and/or the edges 88 c of thebone segments 88 a and 88 b as the mandrel 46 is pulled through theshaft 86 d.

Referring now to FIGS. 14A-D, the cranial fixation assembly 82 and thecranial clamp 84 are illustrated in accordance with still anotherembodiment. In the illustrated embodiment, the axial slots 92 a-d aredefined along a portion of the length of the shaft 86 d between opposingcircumferentially solid portions 86 g located at the proximal and distalends 86 e and 86 f of the shaft 86 d, respectively. The sections of theshaft 86 d defined between the opposing circumferentially solid portions86 g and the axial slots 92 a-d can be hinged in one or more locationsalong their respective lengths, forming one or more jointed legssections of jointed legs 98 a-d. The jointed legs 98 a-d can beconfigured to define one or more bone engagement structures, such ascutting tips 100 a-d, the cutting tips 100 a-d configured to cut intounderlying structure of the bone segments 88 a and 88 b. In theembodiment illustrated in FIGS. 14A-B, the jointed legs 98 a-d are ofsuch a length that when the cranial clamp 84 is disposed within asurgical site, the cutting tips 100 a-d define radial insertiontrajectories that approximately bisect the edges 88 c of the bonesegments 88 a and 88 b. Such trajectories can be used to direct thecutting tips into cancellous bone. In the alternative embodimentillustrated in FIGS. 14C-D, the jointed legs 98 a-d are of such a lengththat when the cranial clamp 84 is disposed within a surgical site, thecutting tips 100 a-d define insertion trajectories into the lower, orinner, surfaces of the bone segments 88 a and 88 b. It should beappreciated that the jointed legs 98 a-d can be configured so as todefine any alternate insertion trajectory into the bone segments 88 aand 88 b as desired.

During use, the illustrated embodiments of the cranial fixation assembly82 can be used to secure bone segments 88 a and 88 b. Once a respectivecranial fixation assembly 82 is disposed in a desired location, adownward, or caudal, biasing force is applied to the upper surface 86 bof the cranial clamp 84, for example by an insertion instrument. Anupward, or cranial, force is applied to the elongate shaft 40 of theexpansion member 26, thereby drawing the mandrel 46 into the distal end86 f of the shaft 86 d. As the mandrel 46 enters the distal end 86 f ofthe shaft 86 d, the outer surface 48 of the mandrel 46 interferes withthe lower of the opposing circumferentially solid portions 86 g, causingthe jointed legs 98 a-d to collapse in upon each other, thereby drivingthe cutting tips 100 b and 100 d into the bone segments 88 a and 88 b,as depicted in FIG. 14B or 14D. As the mandrel 46 advances further intothe shaft 86 d and the cutting tips 100 b and 100 d are driven furtherinto the bone segments 88 a and 88 b, thereby anchoring the cranialclamp 84 within the gap between the bone segments 88 a and 88 b.Additionally, the continued collapsing of the jointed legs 98 a-d candraw the lower surface 86 c of the cranial implant 84 against the outersurfaces of the bone segments 88 a and 88 b, imparting a compressive, orclamping, force between the upper surfaces of the bone segments 88 a and88 b engaged by the lower surface 86 c of the cranial implant 84 and thejointed legs 98 b and 98 d. It should be appreciated that while theillustrated embodiment depicts only the cutting tips 100 b and 100 dengaging the bone segments 88 a and 88 b, the jointed legs 98 a-d can beso configured, and the cranial fixation assembly 82 can be so orientedduring insertion, that any combination of one or more, including all, ofthe cutting tips 100 a-d cut into the bone segments 88 a and 88 b as themandrel 46 is pulled through the shaft 86 d.

Referring now to FIGS. 15A-C, the cranial fixation assembly 82 and thecranial clamp 84 are illustrated in accordance with yet anotherembodiment. In the illustrated embodiment, the axial slots 92 a-d aredefined along a portion of the length of the shaft 86 d between thelower surface 86 c of the cranial cap 84 and an opposingcircumferentially solid portion 86 g located at the distal end 86 f ofthe shaft 86 d, respectively. Each of flexible legs 102 a-d, defined bythe axial slots 92 a-d, extend in a downward, or caudal, direction fromthe lower surface 86 c, bend back upon themselves to form engagementloops 106 a-d, and terminate in the circumferentially solid portion 86g, forming exterior collar surfaces 104 a-d, the collar surfaces 104 a-dconfigured to engage with a neck 108 defined at the proximal end 86 e ofthe shaft 86 d. The outer surface of the engagement loops 106 a-d haveone or more bone engagement structures formed thereon, such as teeth110, the teeth 110 configured to cut into underlying structure of thebone segments 88 a and 88 b.

During use, the illustrated embodiment of the cranial fixation assembly82 can be used to secure bone segments 88 a and 88 b. Once a respectivecranial fixation assembly 82 is disposed in a desired location, adownward, or caudal, biasing force is applied to the upper surface 86 bof the cranial clamp 84, for example by an insertion instrument. Anupward, or cranial, force is applied to the elongate shaft 40 of theexpansion member 26, thereby drawing the mandrel 46 into the distal end86 f of the shaft 86 d. As the mandrel 46 enters the distal end 86 f ofthe shaft 86 d, the outer surface 48 of the mandrel 46 interferes withthe circumferentially solid portion 86 g, causing the circumferentiallysolid portion 86 g to be drawn upward and causing the flexible legs 102a-d to collapse upon themselves such that the teeth 110 of theengagement loops 106 b and 106 d engage the bone segments 88 a and 88 b,cutting into the edges 88 c thereof.

As the mandrel 46 advances further, the teeth 110 are driven furtherinto the edges 88 c of the bone segments 88 a and 88 b, therebyanchoring the cranial clamp 84 within the gap between the bone segments88 a and 88 b. Additionally, the collapsing of the flexible legs 102 a-dcan draw the lower surface 86 c of the cranial implant 84 against theouter surfaces of the bone segments 88 a and 88 b, imparting acompressive, or clamping, force between the upper surfaces of the bonesegments 88 a and 88 b engaged by the lower surface 86 c of the cranialimplant 84 and the flexible legs 102 b and 102 d. As the mandrel 46advances near the aperture 86 a at the proximal end 86 e of the shaft,the collar surfaces 104 a-d can engage the inner surfaces of the neck108, thereby creating a friction force that activates the flexible legs102 a-d into a locked configuration.

In an alternative embodiment depicted in FIG. 15C, the circumferentiallysolid portion 86 g is of sufficient length that it protrudes from theaperture 86 a when the mandrel 46 has been pulled through the shaft 86d. The protruding portion of the circumferentially solid portion 86 gcan have helical threads 111 formed along its outer surface at thedistal end 86 f of the shaft 86 d, the threads 111 configured to engagewith complimentary threads of a locking nut 112. The locking nut 112 canbe installed on the distal end 86 f of the shaft 86 d in order toprevent the collar surfaces 104 a-d of the circumferentially solidportion 86 g from backing out of the neck 108, thereby activating theflexible legs 102 a-d to an unlocked configuration. It should beappreciated that while the illustrated embodiment depicts only theengaging loops 106 b and 106 d engaging the bone segments 88 a and 88 b,the flexible legs 102 a-d can be so configured, and the cranial fixationassembly 82 can be so oriented during insertion, that any combination ofone or more, including all, of the engagement loops 106 a-d engage thebone segments 88 a and 88 b as the mandrel 46 is pulled through theshaft 86 d. If it is subsequently desired to distract the cranial clamp84 from a surgical site, the flexible legs 102 a-d can be activated toan unlocked configuration by depressing the circumferentially solidportion 86 g downward and out of the neck 108 (having first removed thelocking nut 112 if applicable). When the flexible legs 102 a-d are inthe unlocked configuration, the cranial clamp 84 can be removed.

Referring now to FIGS. 16A-G, the cranial fixation assembly 82 and thecranial clamp 84 are illustrated in accordance with still anotherembodiment. In the illustrated embodiment, the shaft 86 d iscircumferentially solid along its entire length between the proximal anddistal ends 86 e and 86 f, respectively. The body 86 of the cranialclamp 84 further includes a bottom disc 86 h formed at the distal end 86f thereof. The bottom disc 86 h can have one or more bone engagementstructures extending radially therefrom, such as points 114, the points114 configured to cut into or otherwise engage with the bone segments 88a and 88 b as described in more detail below. In the illustratedembodiment, five points 114 are spaced apart equally around thecircumference of the bottom disc 86 h, but more or less points 114 couldbe circumferentially arranged in any pattern on the bottom disc 86 h asdesired. The outer surface of the shaft may have optional boneengagement structures, such as teeth 116, formed thereon, the teeth 116configured to engage the edges 88 c of the bone segments 88 a and 88 b.The thickness of the shaft 86 d, defined by the outer and innerdiameters OD3 and ID4 of the shaft 86 d, can be configured to allowvarying degrees of axial compression as the mandrel 46 is pulled thoughof the shaft 86 d. A greater degree of axial compression allows theshaft 86 d of the cranial clamp 84 to be manufactured in such a lengththat the cranial fixation system 82 can be utilized to secure bonesegments of a variety of thicknesses.

During use, the cranial fixation assembly 82 can be used to secure bonesegments 88 a and 88 b. Once a respective cranial fixation assembly 82is disposed in a desired location, a downward, or caudal, biasing forceis applied to the upper surface 86 b of the cranial clamp 84, forexample by an insertion instrument. An upward, or cranial, force isapplied to the elongate shaft 40 of the expansion member 26, therebydrawing the mandrel 46 into the distal end 86 f of the shaft 86 d. Inthe embodiment depicted in FIGS. 16A-B, as the mandrel 46 enters thedistal end 86 f of the shaft 86 d, the outer surface 48 of the mandrel46 interferes with the inner surface of the shaft 86 d, causing theshaft 86 d to compress axially towards the proximal end 86 e and/or toexpand radially outward as described above. Axial compression of theshaft 86 d causes the points 114 to be drawn upwards and to engage withthe lower surfaces of the bone segments 88 a and 88 b, thereby drawingthe lower surface 86 c of the cranial implant 84 against the outersurfaces of the bone segments 88 a and 88 b, and imparting acompressive, or clamping, force onto the surfaces of the bone segments88 a and 88 b disposed between the lower surface 86 c of the cranialimplant 84 and the points 114. Radial expansion of the shaft 86 d cancause the outer surface of the shaft 86 d, and optional teeth 116 ifpresent, to engage the edges 88 c of the bone segments 88 a and 88 b,thereby inducing a friction fit of the cranial clamp 84 within the gapbetween the bone segments 88 a and 88 b. It should be appreciated thatthe lower disc 86 h can be formed without the points 114, for example toaugment the amount of available surface area of the lower disc 86 h forengaging with the lower surfaces of the bone segments 88 a and 88 b.

In an alternative embodiment as depicted in FIGS. 16D-E, the cranialfixation assembly further includes an auxiliary fixation member, such asa spreading disc 115, the spreading disc 115 configured to be carried bythe points 114. The spreading disc has an outer diameter that is smallerthan the width of the gap between the bone segments 88 a and 88 b, andan inner diameter that is greater than the shaft 86 d, such that thespreading disc 115 does not inhibit radial expansion of the shaft 86 das the mandrel 46 is pulled therethrough. The shaft 86 d is of such alength that the spreading disc 115 can be carried around the shaft 86 dby the points 114, while leaving a volume between the lower surface 86 cof the cranial implant 84 and the spreading disc 115 that is filled withan deformable engagement material, such as a filler 117. The engagementmaterial can act as an adhesive, or may otherwise provide addedstructural integrity to the expandable cranial fixation assembly. Forexample, the filler 117 may be made of an elastomeric material, anosteoinductive material, a combination thereof, or any other suitablematerial as desired. It should be appreciated that the lower disc 86 hcan be formed without the points 114, for example to augment the amountof available surface area of the lower disc 86 h for engaging with thespreading disc 115.

During use, as the mandrel 46 enters the distal end 86 f of the shaft 86d, the outer surface 48 of the mandrel 46 interferes with the innersurface of the shaft 86 d, causing the shaft 86 d to axially compressand/or expand radially outward as described above. Axial compression ofthe shaft 86 d causes the spreading disc 115 to be drawn upward in thedirection of the lower surface 86 c of the cranial clamp 84, therebycompressing the filler 117 such that it expands radially outward betweenthe cranial clamp 84 and the spreading disc 115, and engages the edges88 c of the bone segments 88 a and 88 b, thereby securing the cranialclamp 84 within the gap between the bone segments 88 a and 88 b. As themandrel 46 advances further up the shaft 86 d, the lower surface 86 c ofthe cranial implant 84 is drawn against the outer surfaces of the bonesegments 88 a and 88 b, thereby imparting a compressive, or clamping,force between the upper surfaces of the bone segments 88 a and 88 bengaged by the lower surface 86 c of the cranial implant 84 and thefiller 117 engaged along the edges 88 c of the bone segments 88 a and 88b.

In another alternative embodiment as depicted in FIGS. 16F-G, the shaft86 d is of a thickness such that axial compression during pull-though ofthe mandrel is minimized, and is of such a length that when the cranialclamp 84 is disposed within a surgical site, the points 114 defineinsertion trajectories into the edges 88 c of the bone segments 88 a and88 b. In this embodiment, as the mandrel 46 enters the distal end 86 fof the shaft 86 d, the outer surface 48 of the mandrel 46 interfereswith the inner surface of the shaft 86 d, causing the shaft 86 d toexpand radially outward as described above. Radial expansion of theshaft 86 d causes the points 114 to cut into the edges 88 c of the bonesegments 88 a and 88 b, for example into cancellous bone, therebysecuring the cranial clamp 84 within the gap between the bone segments88 a and 88 b. As the mandrel 46 advances further up the shaft 86 d, thelower surface 86 c of the cranial implant 84 is drawn against the outersurfaces of the bone segments 88 a and 88 b, thereby imparting acompressive, or clamping, force between the upper surfaces of the bonesegments 88 a and 88 b engaged by the lower surface 86 c of the cranialimplant 84 and the points 114 engaged in the edges 88 c of the bonesegments 88 a and 88 b. As the mandrel 46 is drawn through the shaft 86d, the shaft 86 d undergoes radial expansion. It should be noted thatthe shaft 86 d can be designed to limit or restrict the amount of axialcompression towards the proximal end 86 e, for example by tapering thethickness of the shaft 86 d between the proximal and distal ends 86 eand 86 f, and the like.

Referring now to FIGS. 17A-G, the cranial fixation assembly 82 and thecranial clamp 84 are illustrated in accordance with yet anotherembodiment. In the illustrated embodiment, the shaft 86 d defines anoblong radial cross section, and is circumferentially solid along itsentire length between the proximal and distal ends 86 e and 86 f,respectively, of the body 86. The outer surface of the shaft 86 d hasbone engagement structures, such as raised ridges 118, formed thereon.Furthermore, the aperture 86 a is extended as an axial bore through theentirety of the shaft 86 d along a concentric longitudinal axis C thatis offset from the central shaft axis S.

During use, the cranial fixation assembly 82 can be used to secure bonesegments 88 a and 88 b. The oblong shape of the shaft 86 d allows forthe cranial clamp 84 to be optionally pre-fixed in a desired insertionposition before the mandrel 46 is pulled through. This is accomplishedby inserting the cranial fixation assembly 82 into a gap between bonesegments 88 a and 88 b such that the narrow portion of the oblong shaft86 d is disposed in the gap between the bone segments 88 a and 88 b, asdepicted in FIG. 17B. The cranial fixation assembly 82 can then berotated in either a clockwise, or counter clockwise, direction, so thatwider portion of the oblong shaft 86 d, and the raised ribs 118 formedthereon, engages the edges 88 c, for example at engagement points 120,of the bone segments 88 a and 88 b, as depicted in FIG. 17C. Of coursethe cranial fixation assembly 82 can be repositioned before the mandrel46 is pulled through by counter-rotating the cranial implant 84 todisengage the raised ribs 118, positioning the cranial fixation assembly82 in the new desired location, and pre-fixing it within the newlocation as described above.

Once the cranial fixation assembly 82 is disposed in the desiredlocation, a downward, or caudal, biasing force is applied to the uppersurface 86 b of the cranial clamp 84, for example by an insertioninstrument. An upward, or cranial, force is applied to the elongateshaft 40 of the expansion member 26, thereby drawing the mandrel 46 intothe distal end 86 f of the shaft 86 d. In the embodiment depicted inFIGS. 17D-E, as the mandrel 46 enters the distal end 86 f of the shaft86 d, the outer surface 48 of the mandrel 46 interferes with the innersurface of the shaft 86 d, causing the shaft 86 d to expand radiallyoutward as described above. Radial expansion of the shaft 86 d causesthe outer surface of the shaft 86 d and the raised ridges 118 to engagethe edges 88 c of the bone segments 88 a and 88 b, thereby inducing afriction fit of the cranial clamp 84 within the gap between the bonesegments 88 a and 88 b.

In an alternative embodiment depicted in FIGS. 17F-G, the disc shapedportion of the body 86 is omitted, and the wall thickness of the shaft86 d, defined by the outer and inner diameters OD3 and ID4 of the shaft86 d, is thicker at the proximal and distal ends 86 e and 86 f of theshaft 86 d than in the intermediate portion of the shaft 86 d betweenthe proximal and distal ends 86 e and 86 f. During use, the cranialclamp 84 is disposed within a gap between the bone segments 88 a and 88b, and pre-fixed in position, as described above. As the mandrel 46 isdrawn up and enters the distal end 86 f of the shaft 86 d, the outersurface 48 of the mandrel 46 interferes with the inner surface of theshaft 86 d, causing the shaft 86 d to expand radially outward asdescribed above. Radial expansion of the shaft 86 d causes the outersurface of the shaft 86 d and the raised ridges 118 to engage the edges88 c of the bone segments 88 a and 88 b, thereby inducing a friction fitof the cranial clamp 84 within the gap between the bone segments 88 aand 88 b. Additionally, as the mandrel 46 is pulled through and radiallyexpands the shaft 86 d, the thicker portions of the shaft 86 d at theproximal and distal ends 86 e and 86 f cause clamping tabs 122 to beformed on the upper and lower surfaces of the bone segments 88 a and 88b. The clamping tabs 122 impart a compressive, or clamping, force ontothe upper and lower surfaces of the bone segments 88 a and 88 b disposedbetween the clamping tabs 122.

Referring now to FIGS. 18A-L, the cranial fixation assembly 82 and thecranial clamp 84 are illustrated in accordance with still anotherembodiment. In the illustrated embodiment, the shaft 86 d iscircumferentially solid along its entire length between the proximal anddistal ends 86 e and 86 f, respectively. The cranial fixation assembly82 further includes an expandable auxiliary fixation member, such as thebottom disc 124. The bottom disc 124 includes a generally disc shapedbody 126 with a convex upper surface 126 a, and an opposing convex lowersurface 126 b. The concavity and convexity of the upper and lowersurfaces 126 a and 126 b, respectively, can be configured to conform toa particular anatomical region, for example a particular area on theinner surface of the skull, so as to maximize contact between the uppersurface 126 a and underlying bone segments 88 a and 88 b, whilesimultaneously minimizing the profile of the lower surface 126 b withrespect to the inner surface of the bone segments 88 a and 88 b. Itshould be noted that any alternative body geometry and/or surfaceprofile can be used for the auxiliary clamping member, examples of whichare described in more detail below.

The body 126 of the bottom disc 124 further includes a ductilecannulated shaft 126 c having a proximal end 126 d and an opposingdistal end 126 e, the shaft 126 d extending in an upward, or cranial,direction from the distal end 126 e at the upper surface 126 a along acentral shaft axis S. The shaft 126 c is configured to be received bythe shaft 86 d of the cranial clamp 84. Accordingly, the outer diameterOD4 of the shaft 126 c is slightly smaller than the inner diameter ID4of the shaft 86 d. The shaft 126 c further includes an axial bore 126 fformed therethrough along the longitudinal shaft axis S. The thicknessof the shaft 126 c is defined by the difference between the outerdiameter OD4 of the shaft and the inner diameter ID5 defined by theaxial bore 126 f. The inner diameter ID5 of the shaft 126 c can be justslightly smaller than the outer dimension of the outer surface 48 of themandrel 46. It should be appreciated that while the illustratedembodiments of the cranial fixation assemblies 82 are described anddepicted in corresponding figures herein with the shaft 126 c of thebottom disc 124 configured to be received within the shaft 86 d of thecranial clamp 84, the components could be configured in a reversefashion, such that the shaft 86 d of the cranial clamp 84 is configuredto be received within the shaft 126 c of the bottom disc 124. Insurgical applications, any variety of these configurations could be usedas desired.

During use, the cranial fixation assembly 82 can be used to secure bonesegments 88 a and 88 b. For example a plurality of bottom discs 124,with corresponding expansion members 26 disposed within the shafts 126 cof the bottom discs, are disposed in desired locations around theperimeter of an opening within a patient's skull. Once the bottom discs124 of the plurality of cranial fixation assemblies 82 are positioned, acorresponding bone flap can be disposed within the skull opening, suchthat the shafts 126 c of the bottom discs 124 are disposed within thegap between the bone flap and the surrounding bone of the skull. Acorresponding plurality of cranial clamps 84 can then be inserted ontorespective expansion members and positioned such that the shafts 126 cof the bottom discs 124 are disposed within the shafts 86 d of thecranial clamps 84.

Once the plurality of cranial fixation assemblies are positioned asdesired, and for each respective cranial fixation assembly 82, adownward, or caudal, biasing force is applied to the upper surface 86 bof the cranial clamp 84, for example by an insertion instrument. Anupward, or cranial, force is applied to the elongate shaft 40 of theexpansion member 26, thereby drawing the mandrel 46 into the axial bore126 f at the distal end 126 e of the shaft 126 c. In the embodimentdepicted in FIGS. 18B-C, as the mandrel 46 enters the distal end 126 eof the shaft 126 c, the outer surface 48 of the mandrel 46 interfereswith the inner surface of the axial bore 126 f, causing the shaft 126 cto compress axially towards the proximal end 126 d and/or to expandradially outward as described above. Axial compression of the shaft 126c causes the shaft 126 c of the bottom disc 124 to enter the shaft 86 dof the cranial clamp 84, and causes the upper surface 126 a of thebottom disc 124 to be drawn upwards and to engage with the lowersurfaces of the bone segments 88 a and 88 b, thereby drawing the lowersurface 86 c of the cranial implant 84 against the outer surfaces of thebone segments 88 a and 88 b, and imparting a compressive, or clamping,force onto the surfaces of the bone segments 88 a and 88 b disposedbetween the lower surface 86 c of the cranial implant 84 and the uppersurface 126 a of the bottom disc 124. As the mandrel 46 advances withinthe shaft 126 c, the shaft 126 c radially expands and engages with theshaft 86 d of the cranial clamp 84, which in turn causes the shaft 86 dto expand radially, thereby causing the outer surface of the shaft 86 dto engage the edges 88 c of the bone segments 88 a and 88 b, therebyinducing a friction fit of the bottom disc 124 and the cranial clamp 84within the gap between the bone segments 88 a and 88 b and fixing thebottom disc 124 and the cranial clamp 84 with respect to each other.

In an alternative embodiment as depicted in FIGS. 18D-F, the body 126 ofthe bottom disc 124 is configured with a plurality of bone engagementstructures, such as points 128, that are formed within the disc shapedportion of the body 126, as illustrated in FIG. 18F. The points 128 areconfigured to cut into or otherwise engage with the bone segments 88 aand 88 b, as described in more detail below. In the illustratedembodiment, six points 128 are spaced apart equally around thecircumference of the bottom disc 124, but more or less points 128 couldbe circumferentially arranged in any pattern on the bottom disc 124 asdesired. The outer surface of the shaft 126 c and the inner surface ofthe shaft 86 d may have optional engagement structures, such as raisedridges 130, formed thereon, the raised ridges 130 configured tocomplimentarily engage each other as the shaft 126 c of the bottom disc124 enters the shaft 86 d of the cranial clamp 84. Of course otherengagement structures, such as ratcheting teeth, or the like, could beused as desired. Use of the optional raised ridges 130 on the shafts 126c and 86 d of the bottom disc 124 and/or the cranial clamp 84 allowthose components to be manufactured in such a length that the cranialfixation system 82 can be utilized to secure bone segments of a varietyof thicknesses. Additionally, the shaft 126 c is of such a length thatwhen the bottom disc 124 is disposed within the shaft 86 d of thecranial clamp 84 within a surgical site, the points 128 define insertiontrajectories into the edges 88 c of the bone segments 88 a and 88 b.

In the embodiment depicted in FIGS. 18D-F, as the mandrel 46 enters thedistal end 126 e of the shaft 126 c and, the outer surface 48 of themandrel 46 interferes with the inner surface of the axial bore 126 f,causing the shaft 126 c to expand radially outward as described above.Radial expansion of the shaft 126 c causes the points 128 to cut intothe edges 88 c of the bone segments 88 a and 88 b, thereby securing thebottom disc 124 within the gap between the bone segments 88 a and 88 b.As the mandrel 46 advances further up the shaft 126 c, the lower surface86 c of the cranial implant 84 is drawn against the outer surfaces ofthe bone segments 88 a and 88 b, thereby imparting a compressive, orclamping, force between the upper surfaces of the bone segments 88 a and88 b engaged by the lower surface 86 c of the cranial implant 84 and thepoints 128 engaged in the edges 88 c of the bone segments 88 a and 88 b.

In another embodiment, alternative expandable auxiliary fixation memberscan be provided, for example the key lock bars 132, as illustrated inFIGS. 18G-L. The key lock bars 132 are constructed similarly to thebottom discs 124, with the disc shaped portion of the body 126 replacedby one or more wings 134. The wings are configured so as to allow thecranial fixation assembly to be distracted from a patient's skull, forexample by inserting a distraction tool into the axial bore 126, androtating the key lock bar 132 so that the blades 134 are oriented withinthe gap between the bone segments 88 a and 88 b, as illustrated in FIGS.18H, 18J, and 18L. Thereafter, the cranial fixation assembly 82 can beeasily removed from the skull. It should be appreciated that althoughthe illustrated embodiments depict one, two, or four rectangular, planarblades 134, that any blade geometry and/or number of blades can be usedas desired. During use, the key lock bars 132 can be secured to the bonesegments 88 a and/or 88 b, so as to prevent rotation of the key lockbars 132 in situ, for example by the use of securing structures, forexample retaining hooks passed through bores in the shaft 126 c and/orthe blades 134 and inserted into the bone segments 88 a and/or 88 b,retaining screws inserted through apertures in the blades 134 and intothe bone segments 88 a and/or 88 b, or the like.

Referring now to FIGS. 19A-F, the cranial fixation assembly 82 and thecranial clamp 84 are illustrated in accordance with yet anotherembodiment. In the embodiment depicted in FIGS. 19A-C, an expandableengagement body, such as the generally rectangular expandable fixationblock 136 extends from the lower surface 86 c of the body 86 in place ofthe shaft 86 d. It should be appreciated that the body of the fixationblock 136 can take on any alternative geometry as desired. The thicknessof the fixation block 136, as defined by the distance between opposingupper and lower ends 136 a and 136 b of the fixation block 136, can bedefined to match the thickness of the bone segments 88 a and 88 b in adesired surgical insertion site. The fixation block 136 has a bore 136c, defined along the longitudinal shaft axis S, extending therethroughbetween opposing front and rear ends 136 d and 136 e, the longitudinalbore 136 c having an inner diameter that is slightly smaller than theouter dimension of the outer surface 48 of the mandrel 46. It should beappreciated that the while a round bore 136 c is depicted in theillustrated embodiment, that any other desired bore geometry can beused. The opposing sides 136 f of the fixation block have boneengagement structures formed thereon, for example in the form ofopposing rows of teeth 138, the teeth 138 configured to engage the bonesegments 88 a and 88 b, for example by cutting into the edges 88 c ofthe bone segments 88 a and 88 b.

During use, the cranial fixation assembly 82 can be used to secure bonesegments 88 a and 88 b. Once a respective cranial fixation assembly 82is disposed in a desired location, a downward, or caudal, biasing forceis applied to the upper surface 86 b of the cranial clamp 84, forexample by an insertion instrument. A lateral force is applied to theelongate shaft 40 of the expansion member 26, thereby drawing themandrel 46 into the bore 136 c at the front end 136 d of the fixationblock 136. The lateral force can be applied, for example, by pulling acable attached to the end of the elongate shaft 40 opposite the mandrel46. As the mandrel 46 enters the bore 136 c, the outer surface 48 of themandrel 46 interferes with the inner surface of the bore 136 c, causingwidthwise expansion of the fixation block 136. As the fixation block 136expands, the sides 136 f of the fixation block engage the edges 88 c ofthe bone segments 88 a and 88 b, causing the teeth 138 on the sides 136f of the fixation block 136 to engage with the edges 88 c of the bonesegments 88 a and 88 b, thereby inducing a friction fit of the cranialclamp 84 within the gap between the bone segments 88 a and 88 b, andanchoring the cranial clamp 84 within the gap between the bone segments88 a and 88 b. As the teeth 138 cut into the edges 88 c of the bonesegments 88 a and 88 b, the lower surface 86 c of the cranial implant 84can be drawn against the outer surfaces of the bone segments 88 a and 88b, thereby imparting a compressive, or clamping, force onto the surfacesof the bone segments 88 a and 88 b disposed between the lower surface 86c of the cranial implant 84 and the teeth 138.

In an alternative embodiment depicted in FIGS. 19D-F, the rows of teeth138 are replaced with alternative bone engagement structures, such as aplurality of spikes 140. The spikes 140 are carried in a respectiveplurality of cross bores 142 that intersect with the bore 136 c andextend between the opposing sides 136 f of the fixation block 136. Thespikes 140 are disposed within the cross bores 142 such that the dullends of the spikes protrude into the bore 136 c, with the pointed endsof the spikes 140 facing the sides 136 f of the fixation block 136.During use, as the mandrel 46 advances through the bore 136 c, the outersurface 48 of the mandrel 46 interferes with the dull ends of the spikes140, thereby causing spikes 140 to translate outwardly within the crossbores 142, such that the pointed ends of the spikes 140 protrude fromthe cross bores 142 on the sides 136 f of the fixation block, and cutinto the edges 88 c of the bone segments 88 a and 88 b, therebyanchoring the cranial clamp 84 within the gap between the bone segments88 a and 88 b. As the spikes 140 cut into the edges 88 c of the bonesegments 88 a and 88 b, the lower surface 86 c of the cranial implant 84can be drawn against the outer surfaces of the bone segments 88 a and 88b, thereby imparting a compressive, or clamping, force onto the surfacesof the bone segments 88 a and 88 b disposed between the lower surface 86c of the cranial implant 84 and the spikes 140.

Referring now to FIGS. 20A-B, the cranial fixation assembly 82 and thecranial clamp 84 are illustrated in accordance with still anotherembodiment. In the illustrated embodiment, the cranial clamp 84 includesan expandable engagement body comprised of ductile upper and lowerfixation members 144 and 146, each of the upper and lower fixationmembers 144 and 146 having opposing proximal and distal ends 144 a and144 b, and 146 a and 146 b, respectively. The fixation members 144 and146 of the illustrated embodiment have annular bodies, but any othersuitable body geometry could be used as desired. The lower fixationmember 146 is configured to be received within the upper fixation member144. In the illustrated embodiment, the upper and lower fixation members144 and 146 have cylindrically shaped bodies, but any other suitablebody geometry could be used as desired. The outer surface of the lowerfixation member 146 can have optional engagement structures configuredto engage the inner surface of the upper fixation member 144 formedthereon, for example raised ridges 148. The inner surface of the upperfixation member 144 can have optional complimentary raised ridges 148formed therein. The inner diameter of the lower fixation member 146 isslightly smaller than the outer dimension of the outer surface 48 of themandrel 46.

The lower fixation member 146 may have a greater length as definedbetween its proximal and distal ends 146 a and 146 b, than the length ofthe upper fixation member 144 as defined between its proximal and distalends 144 a and 144 b. The upper and lower fixation members 144 and 146can be manufactured in varying lengths, for example based on the widthof the gap between the bone segments 88 a and 88 b in which the cranialclamp 84 will be disposed. The proximal end 144 a of the upper fixationmember 144 is connected to the distal end 146 b of the lower fixationmember 146 by one or more flexible curved arms 150. The outer surfacesof the curved arms 150 have bone engagement structures formed thereon,for example teeth 152. In a pre-installed configuration, the proximalend 146 a of the lower fixation member 146 can be engaged within thedistal end 144 b of the upper fixation member 144. It should beappreciated that while the cranial clamp 84 is illustrated as having twoflexible arms 150, any number of flexible arms 150 could be used asdesired, or alternatively, one continuous flexible arm 150 could beformed around the entire perimeter of the upper and lower fixationmembers 144 and 146.

During use, the cranial fixation assembly 82 can be used to secure bonesegments 88 a and 88 b. Once a respective cranial fixation assembly 82is disposed in a desired location, a downward, or caudal, biasing forceis applied against the proximal end 144 a of the upper fixation member144, for example by an insertion instrument. An upward, or cranial,force is applied to the elongate shaft 40 of the expansion member 26,thereby drawing the mandrel 46 into the distal end 146 b of the lowerfixation member 146. As the mandrel 46 advances upwardly within thelower fixation member 146, the upper and lower fixation members 144 and146 are drawn together, thereby causing the flexible arms 150 tocollapse outwardly towards each other such that the teeth 152 engage thebone segments 88 a and 88 b, thereby anchoring the cranial clamp 84within the gap between the bone segments 88 a and 88 b. As the mandrel46 advances through the lower fixation member 146, the lower fixationmember 146 may expand in a radial direction, causing the optional raisedridges 148 on the outer surface of the lower fixation member 146 toengage with the inner surface of the upper fixation member 144, therebyactivating the cranial fixation assembly 82 into a locked configuration.

Referring now to FIGS. 21A-B, the cranial fixation assembly 82 and thecranial clamp 84 are illustrated in accordance with still anotherembodiment. In the illustrated embodiment, the mandrel 46 is pushedinto, rather than pulled through, the shaft 86 d. Additionally, the legs90 a-d have bone engagement structures formed at the distal endsthereof, for example cutting tips 154 a-d. The legs 90 a-d are of such alength that when the cranial clamp 84 is disposed within a surgicalsite, the distal ends of the legs, and consequently the cutting tips 154a-d define insertion trajectories into the edges 88 c of the bonesegments 88 a and 88 b.

During use, the cranial fixation assembly 82 can be used to secure bonesegments 88 a and 88 b. Once a respective cranial fixation assembly 82is disposed in a desired location, the cranial clamp 84 is held inposition, for example by an insertion instrument. A downward, or caudal,force is applied to the elongate shaft 40 of the expansion member 26,thereby causing the mandrel 46 to enter the proximal end 86 e of theshaft 86 d. As the mandrel 46 enters the shaft 86 d, the outer surface48 of the mandrel 46 interferes with the inner surface of the shaft 86d, causing the shaft 86 d to expand radially outward as described above.Radial expansion of the shaft 86 d causes the legs 90 a-d to deflectoutwardly, in turn causing the cutting tips 154 b and 154 d of the legs90 b and 90 d to cut into the edges 88 c of the bone segments 88 a and88 b, thereby securing the cranial clamp 84 within the gap between thebone segments 88 a and 88 b. As the cutting tips 154 b and 154 d of thelegs 90 b and 90 d cut into the bone segments 88 a and 88 b, the lowersurface 86 c of the cranial implant 84 is drawn against the outersurfaces of the bone segments 88 a and 88 b, thereby imparting acompressive, or clamping, force between the upper surfaces of the bonesegments 88 a and 88 b engaged by the lower surface 86 c of the cranialimplant 84 and the legs 90 b and 90 d engaging the edges 88 c of thebone segments 88 a and 88 b via the cutting tips 154 b and 154 d. Itshould be appreciated that while the illustrated embodiment depicts onlythe cutting tips 154 b and 154 d engaging the bone segments 88 a and 88b, the legs 90 a-d can be so configured, and the cranial fixationassembly 82 can be so oriented during insertion, that any combination ofone or more, including all, of the cutting tips 154 a-d cut into thebone segments 88 a and 88 b as the mandrel 46 advances downwardly intothe shaft 86 d.

It should be appreciated that a variety of kits can be provided thatinclude one or more components of the expandable fixation assemblies 20,the expandable cranial fixation assemblies 82, and/or the expandableintervertebral implant assemblies 157. The components of the kits may beconfigured the same or differently. For example, within a single anchorkit, varying numbers of expandable fixation members 24 having variableshaft widths, lengths, and anchoring region profiles may be providedalong with expansion members 26 having varying mandrels 46, and so on,depending for example on the type of procedure being performed by asurgeon, or on the particular anatomies of individual patients. Inanother example, a cranial fixation kit can be provided with a pluralityof expandable cranial clamps 84 in accordance with the variousembodiments described herein. Furthermore, the kits may also beconfigured differently with respect to which components of theindividual systems are included in the kits. For example, a kit ofexpandable fixation assemblies 20 intended for fracture reduction mayinclude one or more fixation members with offset shaft axes in additionto fixation members 24 with central shaft axes. Some of the fixationmembers 24 may have locking features formed on the heads 32 thereof, andthe kit may also include one or more bone plates 62 intended for theparticular type of fracture reduction procedure. In another example, oneor more expandable intervertebral implant assemblies 157, configured thesame or differently, can be provided in a spinal fixation kit along withone or more fixation members 24, one or more traditional pedicle screws,fixation rods, and the like.

Although the expandable fixation members and the other components of theexpandable fixation assembly 20, the expandable cranial fixationassembly 82, and the expandable intervertebral implant assembly 157 havebeen described herein with reference to preferred embodiments and/orpreferred methods, it should be understood that the words which havebeen used herein are words of description and illustration, rather thanwords of limitation. For example, it should be appreciated that thestructures and/or features of components of the expandable fixationassembly 20 may be combined with or otherwise integrated with thestructures and/or features of the expandable intervertebral implantassembly 157, and so on, unless otherwise indicated. Furthermore, itshould be noted that although the expandable fixation assembly 20, theexpandable cranial fixation assembly 82, and the expandableintervertebral implant assembly 157 have been described herein withreference to particular structure, methods, and/or embodiments, thescope of the instant disclosure is not intended to be limited to thoseparticulars, but rather is meant to extend to all structures, methods,and/or uses of the expandable fixation assembly 20, the expandablecranial fixation assembly 82, and the expandable intervertebral implantassembly 157. Those skilled in the relevant art, having the benefit ofthe teachings of this specification, may effect numerous modificationsto the expandable fixation assembly 20, the expandable cranial fixationassembly 82, and the expandable intervertebral implant assembly 157 asdescribed herein, and changes may be made without departing from thescope and spirit of the instant disclosure, for instance as recited inthe appended claims.

What is claimed:
 1. An expandable intervertebral implant assemblyconfigured to be implanted into an intervertebral space between firstand second vertebrae that are spaced from one another along a firstdirection, the assembly comprising: an intervertebral implant comprisingan implant body having upper and lower surfaces configured to face thefirst and second vertebrae, respectively, the upper and lower surfacesspaced from one another along the first direction such that at least aportion of the implant body is solid from the upper surface to the lowersurface, the implant body further having first and second ends that arespaced from one another along a second direction, perpendicular to thefirst direction, the implant body defining at least a first bore thatextends into the first end towards the second end along a bore axis thatextends along the second direction; and a first expansion member,wherein the assembly is configured such that, when the first expansionmember is biased through the first bore along the bore axis in thesecond direction, the first expansion member causes the expandableintervertebral implant assembly to expand along the first direction andengage with the first and second vertebrae, and the assembly isconfigured such that the expandable intervertebral implant assemblyremains expanded after the first expansion member is removed from thefirst bore.
 2. The expandable intervertebral implant assembly of claim1, wherein at least one of the upper and lower surfaces of the implantbody has one or more bone engagement structures formed thereon.
 3. Theexpandable intervertebral implant assembly of claim 2, wherein the boneengagement structures include teeth.
 4. The expandable intervertebralimplant assembly of claim 1, wherein the assembly comprises at least afirst expandable fixation assembly disposed within the first bore,wherein the first expandable fixation assembly includes the firstexpansion member.
 5. The expandable intervertebral implant assembly ofclaim 1, wherein the implant body further includes at least a first slotformed therethrough, the first slot intersecting with the first bore,and wherein the expandable intervertebral implant assembly furtherincludes at least a first pair of engagement structures, the first pairof engagement structures disposed within the first slot on oppositesides of the first expansion member.
 6. The expandable intervertebralimplant assembly of claim 5, wherein: the first pair of engagementstructures includes first and second engagement structures that defineupper and lower bone engagement surfaces, respectively; and when thefirst expansion member is biased through the internal bore, the firstexpansion member causes at least one of the first and second engagementstructures to move away from the other of the at least one of the firstand second engagement structures.
 7. The expandable intervertebralimplant assembly of claim 6, wherein the upper and lower bone engagementsurfaces have bone engagement structures formed thereon.
 8. Theexpandable intervertebral implant assembly of claim 7, wherein the boneengagement structures are teeth.
 9. The expandable intervertebralimplant assembly of claim 4, wherein the first expandable fixationassembly further includes a first fixation member that defines an axialbore, and the first expansion member is disposed within the axial boreof the first fixation member.
 10. The expandable intervertebral implantassembly of claim 1, wherein, the assembly is configured such that, whenthe first expansion member is biased through the first bore, the firstexpansion member causes at least one of the upper and lower surfaces ofthe implant body to move away from the other of the at least one of theupper and lower surfaces of the implant body.
 11. The expandableintervertebral implant assembly of claim 1, wherein the first expansionmember comprises an elongate shaft having a proximal end and an opposingdistal end, and further comprises a mandrel that extends from the distalend.
 12. The expandable intervertebral implant assembly of claim 11,wherein the elongate shaft has a maximum cross-sectional dimension in aselect direction that is perpendicular to an axis of the elongate shaft,and the mandrel has a maximum cross-sectional dimension in the selectdirection that is greater than the maximum cross-sectional dimension ofthe elongate shaft.
 13. The expandable intervertebral implant assemblyof claim 1, wherein: the implant body defines a second bore that extendsinto the first end towards the second end along a second bore axis; andthe assembly further comprises a second expansion member, wherein theassembly is configured such that, when the second expansion member isbiased through the second bore along the second bore axis, the secondexpansion member causes the expandable intervertebral implant assemblyto expand along the first direction and engage with the first and secondvertebrae.
 14. The expandable intervertebral implant assembly of claim13, wherein the second bore is spaced from the first bore along a thirddirection, perpendicular to both the first and second directions. 15.The expandable intervertebral implant assembly of claim 13, wherein thesecond bore is spaced from the first bore along the first direction. 16.An expandable intervertebral implant assembly configured to be implantedinto an intervertebral space between first and second vertebrae that arespaced from one another along a first direction, the assemblycomprising: an intervertebral implant comprising an implant body havingupper and lower surfaces configured to face the first and secondvertebrae, respectively, the upper and lower surfaces spaced from oneanother along the first direction such that at least a portion of theimplant body is solid from the upper surface to the lower surface, theimplant body further having first and second ends that are spaced fromone another along a second direction, perpendicular to the firstdirection, the implant body defining at least a first bore that extendsinto the first end towards the second end along a bore axis; and atleast a first expandable fixation assembly disposed within the firstbore, wherein the first expandable fixation assembly includes a firstexpansion member and includes a first fixation member that defines anaxial bore, the first expansion member being disposed within the axialbore of the first fixation member, wherein: the axial bore of the firstfixation member has an inner dimension, and the first expansion memberhas an outer dimension that is greater than the inner dimension suchthat, when the first expansion member is biased through the axial boreof the first fixation member, the first expansion member causes thefirst fixation member to expand; and the assembly is configured suchthat, when the first expansion member is biased through the first borealong the bore axis, the first expansion member causes the expandableintervertebral implant assembly to expand along the first direction andengage with the first and second vertebrae.
 17. The expandableintervertebral implant assembly of claim 16, wherein expansion of thefirst expansion member causes the expandable intervertebral implantassembly to expand.
 18. The expandable intervertebral implant assemblyof claim 16, wherein: the implant body further includes a first slotformed therethrough, the first slot intersecting with the first bore;the expandable intervertebral implant assembly further includes firstand second engagement structures disposed within the first slot onopposite sides of the first expansion member; and when the firstexpansion member is biased through the axial bore of the first fixationmember, expansion of the first expansion member causes at least one ofthe first and second engagement structures to move away from the otherof the at least one of the first and second engagement structures. 19.The expandable intervertebral implant assembly of claim 16, whereinexpansion of the first expansion member causes at least one of the upperand lower surfaces of the implant body to move away from the other ofthe at least one of the upper and lower surfaces of the implant body.